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By Bernd Sebastian Kamps
Stefano Lazzari

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In December 2019, several patients from Wuhan, People’s Republic of China, developed pneumonia and respiratory failure reminiscent of the SARS epidemic in 2003 (WMHC 2019, www.SARSReference.com). In early January 2020, a new virus was isolated from bronchoalveolar lavage fluid samples and found to be a betacoronavirus (Zhou 2020). Between then and the time of this writing (7 June), the virus, later denominated SARS-CoV-2, has spread to every corner of the world. Millions have been diagnosed with SARS-CoV-2 infection and hundreds of thousands of people have died of COVID-19, the disease caused by SARS-CoV-2. SARS-CoV-2 has the potential to cause a long-lasting pandemic with high fatality rates.

In this chapter, we will discuss:

  • Hotspots of SARS-CoV-2 infection
  • The natural course of the COVID-19 pandemic and its mitigation by “lockdown” measures
  • The effect of “lockdown” measures
  • Special aspects of the pandemic in selected places
  • A ‘COVID pass’
  • The second wave

The transmission of SARS-CoV-2 is discussed in a separate chapter (page 71) which highlights that SARS-CoV-2 is easily transmissible both by symptomatic and asymptomatic individuals; it thrives in closed and densely inhabited environments; and is amplified by so-called ‘superspreader’ events. There is evidence that in China, human-to-human transmission has occurred among close contacts since the middle of December 2019 (Li Q 2020). In Italy and France, SARS-CoV-2 was circulating as early as January among asymptomatic or paucisymptomatic people (Cereda 2020, Gámbaro 2020). In the Greater Paris Region, after retesting samples from 24 patients treated in December and January, one sample collected on  December 27 was retrospectively found to be positive for COVID (France 24, 5 May 2020). The samples had initially been collected to detect flu using PCR tests.

The mean incubation period of SARS-CoV-2 infection is around 5 days (Li 2020, Lauer 2020, Nie X 2020). The serial interval – defined as the duration of time between a primary case-patient having symptom onset and a secondary case-patient having symptom onset – has been estimated to be between 5 and 7.5 days (Cereda 2020). SARS-CoV-2 is highly contagious, with an estimated basic reproduction number R0 of around 2.5-3.0 (Chan 2020, Tang B 2020, Zhao 2020). [R0 indicates the average number of infections one case can generate over the course of the infectious period in a naïve, uninfected population.]

Transmission Hotspots

The probability of SARS-CoV-2 transmission is a function of time and closeness of contact between infected and susceptible individuals. The following settings are catalyzers of local outbreaks:

  • Homes (+ intense social life with friend and colleagues)
  • Workplaces
  • Hospitals
  • Nursing facilities
  • Cruise ships
  • Aircraft carriers and other military vessels
  • Mass gatherings and religious gatherings
  • Schools
  • Prisons
  • Homeless shelters
  • Industrial meat-packing plants
  • Choirs


Infection rates at home varied widely (between 11% and 19%) in three studies (Bi Q 2020, Jing QL 2020, Li W 2020). One group noted that household contacts and those travelling with a COVID-19 case had a 6 to 7 times higher risk of infection than other close contacts, and that children were as likely to be infected as adults (Bi Q 2020). Another group found that the odds of infection among children and young people (<20 years old) was only 0.26 times of that among the elderly (≥60 years old) (Jing QL 2020). A third group calculated that the secondary attack rate in children was 4% compared to 17.1% in adults, and that the secondary attack rate in contacts who were spouses of index cases was 27.8% compared to 17.3% in other adult members in the households (Li W 2020). It has been objected that these transmission rates may be an underestimate if index cases were isolated outside of the home (Sun 2020). In yet another study, 32.4% (48 of 148) of household contacts of 35 index cases were infected (Wu J 2020); however, this percentage relied on the assumption that all secondary cases were infected by the index case. In single households, the transmission rates may probably reach 75% or more (Böhmer 2020).


As early as January 2020, SARS-CoV-2 was found to spread during workshops and company meetings (Böhmer 2020). Later, an outbreak of SARS-CoV-2 infection was reported from a call center where 94 out of 216 employees working on the same floor were infected, translating to an attack rate of 43.5% (Park SY 2020). Recently, outbreaks with hundreds of infected individuals were reported from meat-packing plants in Germany (DER SPIEGEL), the US (The Guardian) and France (Le Monde).

Particularly instructive is the case of a scientific advisory board meeting held in Munich, Germany, at the end of February. Eight dermatologists and 6 scientists (among them the index patient) met in a conference room of about 70 m2 with a U-shaped set-up of tables separated by a central aisle >1 meter wide. During the meeting that lasted 9.5 hours, refreshments were served in the same room 4 times. In the evening, the participants had dinner in a nearby restaurant and shook hands for farewell, with a few short hugs (no kisses!). Finally, the index patient shared a taxi with three colleagues for about 45 min. The outcome: the index patient infected at least 11 of the 13 other participants. When isolated either in a hospital or at home these individuals infected an additional 14 persons (Hijnen 2020).

In the presence of an infected individual, workplaces can be important amplifiers of local outbreaks epidemics.

Hospitals and other health care centers

There is no doubt that transmission in hospitals and other health care centers (including doctors offices) played a prominent role in the origin and spread of local epidemics, especially in the beginning when suspicion of the disease was low. This is reminiscent of the largest MERS outbreak outside of the Arabian peninsula which occurred in the Republic of Korea in 2015. Of the 186 cases, 184 were infected nosocomially (Korea Centers for Disease Control and Prevention 2015).

Hospitals are a favorable environment for the propagation of SARS-CoV-2 (Wison 2020). In some instances, hospitals could have been even the main COVID-19 hub, as they were rapidly populated by infected patients, facilitating transmission to health workers and uninfected patients (Nacoti 2020). Within the first 6 weeks of the epidemic in China, 1,716 cases among health care workers were confirmed by nucleic acid testing, and at least 5 died (0.3%) (Wu 2020).

One hospital study reports that the virus was widely present in the air and on object surfaces in both the intensive care units and general wards, implying a potentially high infection risk for medical staff. Contamination was greater in ICUs. Virus was found on floors, computer mice, trash cans, sickbed handrails, and was detected in the air up to approximately 4 m from patients (Guo 2020). The virus was also isolated from toilet bowl and sink samples, suggesting that viral shedding in stool could be a potential route of transmission (Young 2020, Tang 2020). However, most of these studies have evaluated only viral RNA. It remains to be seen whether this translates into infectious virus.

Although nosocomial spread of the virus is well documented, appropriate hospital infection control measures can prevent nosocomial transmission of SARS-CoV-2 (Chen 2020). This was nicely demonstrated by the case of a person in her 60s who travelled to Wuhan on Dec 25, 2019, returned to Illinois on Jan 13, 2020, and transmitted SARS-CoV-2 to her husband. Although both were hospitalized in the same facility and shared hundreds (n=348) of contacts with HCWs, nobody else became infected (Ghinai 2020).

However, working in a high-risk department, longer duty hours, and suboptimal hand hygiene after coming into contact with patients, are all associated with an increased risk of infection in health care workers (Ran 2020). At one time, during the early epidemic in March 2020, around half of 200 cases in Sardinia were among hospital and other health care workers. On 14 April, the US CDC reported that 9,282 Health Care Personnel has been infected with SARS-COV-2 in the USA.

The risk factors for SARS-CoV-2 infection in health care workers has recently been summarized in a review. There is evidence that more consistent and full use of recommended PPE measures was associated with decreased risk for infection, suggesting a dose–response relationship. Association was most consistent for masks but was also observed for gloves, gowns, and eye protection, as well as hand hygiene. Some evidence was found that N95 respirators might be associated with higher reduction of risk for infection than surgical masks. Evidence also indicated an association between certain exposures (such as involvement in intubations, direct contact with infected patients, or contact with bodily fluids) (Chou 2020).

SARS-CoV-2 outbreaks can occur everywhere, not only in admission, infectious disease and intensive care units. In a pediatric dialysis unit in Münster (Germany), a healthcare worker infected 7 colleagues, three young patients and one accompanying person (Schwierzeck 2020). A Chinese study of 9,684 healthcare workers (HCW) in Tongji Hospital confirmed a higher rate of infection in non-first-line HCW (93/6.574, 1.4%) when compared to those who worked in fever clinics or wards (17/3110, 0.5%) (Lai X 2020). Those who work in clinical departments other than fever clinics and wards may have neglected to adopt adequate protective measures.

In a well-documented report about nosocomial transmission recently published, a man sought help for coronavirus symptoms on March 9, spending only a few hours at the emergency department of a hospital in Durban, South Africa. He was kept separate in a triage area, but that room was reached through the main resuscitation bay, where a stroke patient occupied a bed. Both patients were seen by the same doctor. After being infected, the stroke patient caused a chain of transmission with 39 patients and 80 staff in 16 different departments being infected, and 15 patients dying. The study found that patients infected few other patients directly. Instead staff members spread the disease from patient to patient and from department to department, perhaps sometimes without becoming infected themselves (Nordling 2020). Strictly enforcing infection control measures and screening hospital staff will be important measures in future waves of COVID-19.

Long-term care facilities

Long-term care facilities are high-risk settings for infectious respiratory diseases. In a skilled nursing facility in King County, Washington, US, 167 cases of COVID-19 were diagnosed within less than three weeks from the identification of the first case: 101 residents, 50 health care personnel and 16 visitors (McMichael 2020) (Table 1).

Among residents (median age: 83 years), the case fatality rate was 33.7%. Chronic underling conditions included hypertension, cardiac disease, renal disease, diabetes mellitus, obesity, and pulmonary disease. The study demonstrates that once introduced in a long-term care facility, often by a care worker or a visitor, SARS-CoV-2 has the potential to spread rapidly and widely, with devastating consequences.

A national survey covering 96% of all long-term care facilities in Italy found that in Lombardy, the epicenter of the epidemic, 53.4% of the 3,045 residents who died between 1 February and 14 April were either diagnosed with COVID-19 or presented flu-like symptoms, a death rate among residents of 6.7%. Among the 661 residents who were hospitalized during the same period, 199 (30%) were found positive by a PCR test. According to WHO estimates, in countries in the European Region up to half of those who have died from COVID-19 were residents in long-term care facilities (see the statement to the press by Hans Henri P. Kluge, WHO Regional Director for Europe). Excess mortality data suggests that in several countries many deaths in long-term care facilities might have occurred in patients not tested for COVID-19, which are often not included in the official national mortality statistics.


Table 1. COVID outbreak in a long-term care facility
(N = 101)
Healthcare personnel
(N = 50)
(N = 16)
Median age (range) 83 (51-100) 43.5 (21-79) 62.5 (52-88)
Female (%) 68.3 76 31.2
Hospitalized (%) 54.5 6.0 50.0
Died (%) 33.7 0 6.2
Chronic underlying conditions (%)
Hypertension 67.3 8.0 12.5
Cardiac disease 60.4 8.0 18.8
Renal disease 40.6 0 12.5
Diabetes mellitus 31.7 10.0 6.2
Obesity 30.7 6.0 18.8
Pulmonary disease 31.7 4.0 12.5


SARS-CoV-2 continues to spread in US nursing homes where approximately 1.3 million Americans reside (CDC 200311). In mid-April, more than 1,300 facilities had identified infected patients (Cenziper 2020). As most residents have one or more chronic underling condition such as hypertension, cardiac disease, renal disease, diabetes mellitus, obesity and pulmonary disease, COVID-19 puts them at high risk for premature death.

Cruise ships

Cruise ships carry many people in confined spaces. On 3 February 2020, 10 cases of COVID-19 were reported on the Diamond Princess cruise ship. Within 24 hours, all sick passengers were isolated and removed from the ship and the rest of the passengers quarantined on board. Over time, more than 700 of 3,700 passengers and crew tested positive (around 20%). One study suggested that without any intervention 2,920 individuals out of the 3,700 (79%) would have been infected (Rocklov 2020). The study also showed that an early evacuation of all passengers on 3 February would have been associated with only 76 infected.

For cruise ships, SARS-CoV-2 may spell disaster as carrying village-loads of people from one place to another may not be a viable business model until the global availability of a safe and efficient vaccine.

Aircraft carriers and other military vessels

Big navy vessels such as aircraft carriers can become floating petri dishes for emerging viral respiratory diseases. Already in 1996, an outbreak of influenza A (H3N2) occurred aboard a navy ship. At least 42% of the crew became ill within few days, although 95% had been appropriately vaccinated (Earhart 2001). Since the beginning of the year, several outbreaks of COVID-19 on military ships have been reported, facilitated by the small enclosed areas of work and the lack of private quarters for the crew. The largest outbreaks have been reported on the USS Theodore Roosevelt and the French aircraft carrier Charles de Gaulle. During the Theodore Roosevelt outbreak in late March, around 600 sailors out of a crew of 4,800 were infected with SARS-CoV-2 (see also the March 30 entry of the Timeline); around 60% remained asymptomatic. One active duty sailor died (USNI News). On the French aircraft carrier Charles-de-Gaulle, a massive epidemic was confirmed on 17 April. Among the 1,760 sailors, 1,046 (59%) were positive for SARS-CoV-2, 500 (28%) presented symptoms, 24 (1.3%) sailors were hospitalized, 8 on oxygen therapy and one in intensive care.

Smaller clusters have also been reported on 5 other US military vessels, and in one each from France, Taiwan, and Holland. However, given usual security policies and communication restrictions of national armies and navies, it is possible that other unreported cluster of cases and even deaths might have occurred.

For aircraft carriers, the potential for further outbreaks at any time might well interfere with full operability.

Mass gatherings

Several mass gathering events have been associated with explosive outbreaks of COVID-19. As of April 24, 2020, a total of 5,212 coronavirus cases were related to an outbreak at the Shincheonji Church in South Korea, accounting for about 48.7% of all infections in the country.

A football match played in Milan, Italy on 19 February 2020 has been described as “Game zero” or “a biological bomb”. The match was attended by 40,000 fans from Bergamo and 2,500 from Valencia and played just two days before the first positive case of COVID-19 was confirmed in Italy. 35 percent of Valencia’s team members tested positive for the coronavirus a few weeks later, as did several Valencia fans. By mid-March, there were nearly 7,000 people in Bergamo who had tested positive for the coronavirus with more that 1,000 deaths, making Bergamo the most heavily hit province during the COVID-19 outbreak in Italy. Valencia also had 2,600 cases of the infection.

The annual gathering of the Christian Open Door Church held between 17 and 24 February in Mulhouse, France, was attended by about 2,500 people and became the first significant cluster in France. After a parishioner and 18 family members tested positive on 1 March, a flurry of reported cases brought the existence of a cluster to light. According to an investigative report by France Info, more than 1,000 infected members from the rally in Mulhouse contributed to the start of the COVID-19 epidemic in France. A large number of diagnosed cases and deaths in France as well as Switzerland, Belgium and Germany were linked to this gathering.

Religious celebrations

One report describes 35 confirmed COVID-19 cases among 92 attendees at church events during March 6–11. The estimated attack rates ranged from 38% to 78% (James 2020). In Frankfurt, Germany, one of the first post-lockdown clusters started during a religious ceremony held on 10 May. As of 26 May, 112 individuals were confirmed to be infected with SARS-CoV-2 (Frankfurter Rundschau).

The bottom line: Going to church does not protect from SARS-CoV-2.

Schools and schoolchildren

Schoolchildren usually play a major role in the spread of respiratory viruses, including influenza. However, while the SARS-CoV-2 virus has been detected in many children, they generally experience milder symptoms than adults, need intensive care less frequently and have a low death rate.

The possible role of children in SARS-COV-2 transmission is still unclear. In a small COVID-19 cluster detected in the French Alps at the end of January, one person returning from China infected eleven other people, including a nine-year-old schoolboy. The researchers closely tracked and tested all contacts (Danis 2020). The boy had gone to school after showing COVID-19 symptoms and was estimated to have had more than sixty high-risk close contacts. No one was found positive to the coronavirus, though many had other respiratory infections. Also, no virus was found in the boy’s two siblings who were on the same Alpine vacation. The researchers concluded that “because children are less likely to become infected and symptoms are milder, they may play a less important role in the spread of the new virus”.

A Norwegian Institute of Public Health review of the role of children in the transmission of SARS-CoV-2 found five documented cases of likely spread of disease from children, but concluded that the evidence is sparse and it is too early to say if children play an important role in the spread of the disease (Fretheim 2020). However, a pre-print study of SARS-CoV-2 viral load by patient age conducted by the Institute of Virology, Charité-Universitätsmedizin Berlin, did not find any statistical difference in viral load in different age groups, concluding that children may be as infectious as adults and suggesting to use caution in the re-opening of schools and kindergartens in the present situation (Jones 2020).  The debate continues.


According to the WHO, people deprived of their liberty, such as people in prisons and other places of detention, are more vulnerable to the coronavirus disease (COVID-19) outbreak (WHO 200315). People in prison are forced to live in close proximity and thus may act as a source of infection, amplification and spread of infectious diseases within and beyond prisons. The global prison population is estimated at 11 million and prisons are in no way “equipped” to deal with COVID-19 (Burki 2020). The UN High Commissioner for Human Rights, Michelle Bachelet, has encouraged governments to release inmates who are especially vulnerable to COVID-19, such as older people, as well as low-risk offenders, and a number of countries are taking action to try to reduce the prison population.

As of 21 April, SARS-CoV-2 was present in US correctional and detention facilities. Aggregated data on cases from 37 of 54 state and territorial health department jurisdictions revealed 4,893 cases and 88 deaths among incarcerated and detained persons and 2,778 cases and 15 deaths among staff members (Wallace 2020).

Homeless shelters

Testing in 1,192 residents and 313 staff members in 19 homeless shelters from 4 US cities (see table), initially triggered by the identification of a COVID-19 cluster, found infection rates of up to 66% (Mosites 2020).

In another report from Boston, Massachusetts, 147/408 (36%) homeless shelter residents were positive. Of note, 88% had no fever or other symptoms at the time of diagnosis (Baggett 2020).

Industrial meat-packing plants

On 5 May 2020, the German magazine DER SPIEGEL reported that more than 600 employees were infected with SARS-CoV-2 at meat processing plants in Germany. One week later, The Guardian reported that almost half of the current COVID-19 hotspots in the US were linked to meat processing plants where poultry, pigs and cattle are slaughtered and packaged. At the same time, around a hundred people tested positive in two meat processing plants in France (Le Monde).

Promiscuity, cold and humid conditions are currently favored as explanations for these unusual outbreaks.


On 8 March 2020, the Amsterdam Mixed Choir gave a performance of Bach’s St John Passion in the city’s Concertgebouw Auditorium. Days later, the first singers developed symptoms and in the end 102 of 130 choristers were confirmed to have COVID-19. One 78-year-old choir member died, as did three colleagues; some singers required intensive care (The Guardian, 17 May).

On 9 March, members of the Berlin Cathedral Choir meet for their weekly rehearsal. Three weeks later, 32 out of 74 choir members were positive for SARS-CoV-2 (NDR 2020). All recovered.

On 10 March 2020, 61 members of a Skagit County, Washington, choir met for a 2.5-hour practice. A few weeks later, researchers reported that 32 confirmed and 20 probable secondary COVID-19 cases had occurred (attack rate = 53.3% to 86.7%); three patients were hospitalized, and two died. The authors conclude that transmission was likely facilitated by close proximity (within 6 feet) during practice and increased virus diffusion by the act of singing (Hamner 2020).

These data suggest that any noisy, closed and stagnant air environments (e,g, discos, pubs, birthday parties, restaurants, butchering facilities, etc.) where people stand, sit or lie close together and are required to shout for communication are ideal conditions for generating large SARS-CoV-2 outbreaks.

SARS-COV-2 re-activation or re-infection?

In South Korea and elsewhere more than 100 people who had recovered from COVID-19 were retested positive (Ye 2020) and there was concern that patients who recover from COVID-19 may be at risk of reinfection. However, there was no indication that they were contagious. The most likely explanation is that the ‘infection had been reactivated’ in the patients or that the tests picked up non-infective RNA of the virus. Very preliminary data from an animal study (n=2) suggest that that immunity acquired following primary infection may protect upon subsequent exposure to the virus. Infection of rhesus macaques with SARS-CoV-2 and re-infection after recovery showed that there was no viral replication in nasopharyngeal or anal swabs, nor any other signs of COVID-19 disease recurrence (Bao 2020).

Blood Transfusion

After screening 2,430 donations (1,656 platelet and 774 whole blood) with real-time PCR, authors from Wuhan only found plasma samples positive for viral RNA from 4 asymptomatic donors (Chang 2020). It remains unclear whether detectable RNA signifies infectivity. A preliminary report of a study in Dutch blood donors found that in April 2020 around 3% had detectable antibodies against SARS-COV-2 (NLTimes.nl).

In a Korean study, seven asymptomatic blood donors were later identified as COVID-19 cases. None of 9 recipients of platelets or red blood cell transfusions tested positive for SARS-CoV-2 RNA (Kwon 2020). However, more data are still needed before we can conclude that transmission through transfusion is unlikely.

The pandemic

Natural course of a pandemic

The COVID-19 epidemic started in Wuhan, in Hubei province, China, and spread within 30 days from Hubei to the rest of mainland China, to neighboring countries (in particular, South Korea, Hong Kong and Singapore) and west to Iran, Europe and the American continent. The first huge outbreaks occurred in regions with cold winters (Wuhan, Iran, Northern Italy, the Alsace region in France).

Fifty years ago, the course of the COVID-19 pandemic would have been quite different, with slower global spread but high burden due to limited diagnostic and therapeutic capacities and no option of nation-wide lockdowns (see also a report of the influenza pandemics in 1957 and 1968: Honigsbaum 2020). According to one (controversial) simulation, in the absence of interventions and with a mortality rate of around 0.5%, without interventions COVID-19 would have resulted in 7.0 billion infections and 40 million deaths globally during the first year (Patrick 2020). The peak in mortality (daily deaths) would have been observed approximately 3 months after the beginning of local epidemics. Another model predicted that 80% of the US population (around 260 million people) would have contracted the disease. Of those, 2.2 million Americans would have died, including 4% to 8% of those over age 70 (Ferguson 2020).

Despite these dire predictions, some epidemiologists and senior politicians seriously considered implementing only limited mitigating measures, based on two questionable arguments:

  • The country would not have to face the dramatic economic downturn that seems unavoidable in countries and states which opted for strict containment measures (China, Italy, Spain, France, California, New York, to name a few). However, most economists would argue that there would still be an economic downturn due to self-imposed restrictions by the population and businesses, as shown by the major economic impact even in countries with less severe restrictions (e.g., Sweden).
  • After a few months, up to 70% of the population could be naturally immunized (through infection with SARS-CoV-2) and protected against further outbreaks, able to look ahead to the next winter season with an even temper. (However, it is still unclear how long such acquired immunity would last? Maybe only a few months or few years? See the Immunology chapter, page 125).

In mid-March 2020, the prime minister of a former EU country proposed the approach of ‘letting the virus spread until we reach herd immunity’ as the best solution to the epidemic his nation was about to face. The shock treatment: accepting that a large majority of the population would contract the virus, thus developing a collective immunity and preventing future coronavirus epidemics. The estimated figures from simulation models were dire. With a little over 66 million inhabitants, some 40 million people would have been infected, 4 to 6 million could have become seriously ill, 2 million requiring intensive care. Around 400,000 Britons may have died. The prime minister stated: “Many more families are going to lose loved ones before their time.” Faced with the rapid increase of cases and deaths and a public uproar, the PM eventually made a U-turn, implementing strict confinement measures as other countries were doing.

Only one European country, Sweden, has decided to pursue a strategy of limited public health measures (e.g., protection of older age groups, widespread testing, individual social distancing measures) without enforcing strict rules of confinement or business shutdowns. The results will be briefly discussed below on page 51.

Pandemic 2.0: Lockdowns

Fortunately, for now, the world has been spared from a freely circulating SARS-CoV-2. If humanity can change the climate, why shouldn’t we be able to change the course of a pandemic? Although economists warned that unemployment could surpass the levels reached during the Great Depression in the 1930s, at first, almost all governments considered saving hundreds of thousands lives more important than avoiding a massive economic recession. First in China, six weeks later in Italy and another a week later in most Western European countries, more recently in the US and in many other countries in the world, unprecedented experiments of gigantic dimensions were started: ordering entire regions or the whole nation to lockdown. In Italy and Spain, people were ordered to stay home, except for conducting “essential activities” (i.e., purchasing food, medicines, and other basic supplies, going to hospital, or performing essential work). Italians were told to stay at home even on the popular Pasquetta day, Easter Monday, where people usually flock to the seaside or countryside to enjoy a picnic with family and friends. Eventually, Italians were even restricted from moving from one municipality to another.

While there are differences in the implementation of the lockdown from one country to another, some common measures include:

  • Restrictions of movement from home, unless it is strictly necessary (confinement orstayathome” order)
  • Ban on all public mass gatherings, including concerts, festivals, rallies, even religious events (Tian H 2020)
  • Closure of schools and universities
  • Closure of all retail shops, except for those serving primary needs (food, medicines, gas stations, newsstands, etc)
  • Shutting down of all industries and factories, except where providing essential products
  • Border closing with neighbouring countries, international travel bans. In some cases, restrictions of travel within the country outside the area or region of residence.

Lockdowns have been used in the past to control disease outbreaks, usually in limited areas and for limited periods. China was the first country to implement, on 23 January, a strict and total lockdown in a city of 11 million people, later extended to the whole Hubei province (WHO called this “unprecedented in public health history”). The lockdown lasted 2 months.

Italy was the first country to implement a nationwide lockdown to the whole country on 9 March, to be followed by Denmark (11 March), Ireland and Norway (12 March), Spain and Poland (13 March), Switzerland, France, Belgium (17 March) and then most other European countries. By 26 March, 1.7 billion people worldwide were under some form of lockdown, which increased to 3.9 billion people by the first week of April — more than half of the world’s population. Lockdowns in Europe were generely less strict than in China, allowing the continuation of essential services and industries and the circulation of people when justified.

Lockdown outcomes

The expected result of lockdown measures is the breaking of the chain of SARS-CoV-2 transmission, leading to a reduction of the number of new infections, hospitalization and ultimately deaths. This can be measured in different ways, including by the number of

  • SARS-CoV-2 newly infected people
  • Hospital admissions for COVID-19
  • Patients treated in intensive care units (ICU)
  • Deaths

Number of infections

Figure 1 proved as early as four weeks after the Wuhan lockdown that strict containment measures are capable of curbing a SARS-CoV-2 epidemic. The figure presents the Chinese COVID-19 epidemic curves of laboratory-confirmed cases, by symptom onset (blue) and – separately – by date of report (orange). The data were compiled on 20 February 2020, four weeks after the beginning of the containment measures which included a lockdown on nearly 60 million people in Hubei province as well as travel restrictions for hundreds of millions of Chinese citizens. The blue columns show that (1) the epidemic rapidly grew from 10-22 January, (2) reported cases (by date of onset) peaked and plateaued between 23 January and 28 January and (3) steadily declined thereafter (apart from a spike reported on 1 February). Based on these data, we would now expect a decline in reported cases around three weeks after a general lockdown.


Figure 1. The Chinese outbreak in January/February 2020. Epidemic curves by symptom onset and date of report on 20 February 2020 for laboratory confirmed COVID-19 cases for all of China. Modified from Report of the WHO-China Joint Mission on Coronavirus Disease 2019 (COVID-19), 16-24 February 2020. https://www.who.int/publications-detail/report-of-the-who-china-joint-mission-on-coronavirus-disease-2019-(covid-19)


However, the number of newly diagnosed SARS-CoV-2 cases is of limited usefulness since, being closely related to the number of tests being performed, do not reflect the true number of infections that have occurred. To know the true number, the entire population would need to be tested repeatedly which is, of course, impractical. PCR tests are usually performed in symptomatic patients or, in some cases, in close contacts and most asymptomatic cases will be missed. Seroprevalence studies in population samples that are being implemented can provide a better estimate of the number of people who have been infected in the past but will not directly measure the incidence (new infections). Best incidence estimates can only be made by mathematical modelling. Not surprisingly, the first models of the European epidemic revealed that reported COVID-19 cases represent only a fraction of those truly infected. A model based on observed deaths in 11 European countries suggested that true infections were much higher than reported cases (Flaxman 2020). According to the model, as of 28 March, 5.9 million people in Italy and 7 million in Spain could have been SARS-CoV-2-infected (Table 2). Germany, Austria, Denmark, and Norway would have the lowest attack rates (proportion of the population infected). If these assumptions are validated, the true number of cases would outnumber the reported cases on March 28 (Italy: 92,472; Spain: 73,235; France: 37,575) by up to two orders of magnitude

[The data provided by Flaxman et al. immediately invited us in March to do some kitchen epidemiology. First: if on 28 March the number of infected people in Italy was around 6 million (with a credible interval of 2 to 15 million) and if we assumed that 18 days later the total number of deaths in Italy was around 30,000 (the official figure reported on 15 April was 21,645 deaths), the mortality of COVID-19 infection in Italy could be in the range of 0.5% (0.19%-1.6%).


Table 2. Estimates of total population infected as of 28 March 2020
Deaths on 28 March
% of population
Population infected*
1.1% (0.36%-3.1%) 96,800
3.7% (1.3%-9.7%) 425,500
1.1% (0.40%-3.1%) 63,800
3.0% (1.1%-7.4%) 2,010,000
0.2% (0.28%-1.8%) 166,000
9.8% (3.2%-26%) 5,919,200
0.41% (0.09%-1.2%) 21,600
15% (3.7%-41%) 7,035,000
3.1% (0.85%-8.4%) 316,200
3.2% (1.3%-7.6%) 275,200
2.7% (1.2%-5.4%) 1,798,200
*mean (95% credible interval)

Data source: Flaxman S et al. (Imperial College COVID-19 Response Team). Report 13: Estimating the number of infections and the impact of non-pharmaceutical interventions on COVID-19 in 11 European countries. 30 March 2020. DOI: https://doi.org/10.25561/77731


Second: if at the end of March, around 60% of all deaths in Italy were reported from Lombardy, 60% of the 6 million projected Italian SARS-CoV-2 infections – 3.6 million – would have occurred in a region with a population of 10 million. Moreover, 20% of all deaths in Italy were reported from the province of Bergamo alone which has a population of one 1.1 million.]

Seroprevalence studies underway in several European countries and in the US will clarify these figures soon. Preliminary results of a population survey in Los Angeles County released by USC on 20 April that tested 863 adults found that approximately 4.1% had antibodies to the virus (USC News, 20 April 2020). Adjusting for the statistical margin of error it suggested that between 2.8% to 5.6% of the county’s adult population, approximately 221,000 to 442,000 adults, had been infected. That estimate is 28 to 55 times higher than the 7,994 confirmed cases of COVID-19 reported to the county at the time of the study. The number of COVID-related deaths in the county had then surpassed 600. On 13 May, preliminary results from a nationwide coronavirus antibody study showed that about 5% of the overall Spanish population had contracted the virus, with spikes in prevalence of 11.3%. in Madrid and 14.2% and 13.5% in the central regions of Castilla y Leon and Castilla La Mancha. That is about 10 times more than the number of diagnosed cases.

Hospital admissions for COVID-19

Hospitalizations for COVID-19 are usually recorded and reported as part of the regular health care monitoring system. Several countries are regularly reporting the daily number of COVID-19 hospital admissions as an indicator of the trend in the epidemic. The advantage of monitoring hospital admission is that it can detect changes in transmission dynamics more quickly than the more lagged measures of (incidence of) ICU admissions and deaths (mortality rates). However, hospital admissions have limitations (hospital admission criteria may change from place to place and be modified over time) and can be influenced by, for example, the availability of quality home-based care or health system collapse. In addition, many governments are not publicly providing numbers of daily hospital admissions and discharges (Garcia-Basteiro 2020).

Admissions into intensive care units

A more reliable indicator of the epidemic trend is the number of people treated in intensive care units. In France, the number of new hospital ICU admissions peaked on 1 April (Figure 2), while the daily variation in people treated in ICU (the balance between ICU entries and exits; Figure 3) started being negative one week later. However, this indicator can be influenced by the number of ICU beds and trained health personnel available for COVID-19 patients. If overwhelmed, hospitals might be forced to limit the admission to patients with more chances of survival, or patients might die at home (Grasselli 2020).  In most developing countries, the very small number of ICUs will make this indicator of limited use.

Figure 4 shows the daily number of COVID-19 patients treated in ICU units in France.


Figure 2. Daily number of new hospital ICU admissions for COVID-19 (y-axis: Nouvelles admissions en réanimation).
Source: Pandémie de Covid-19 en France, Wikipedia.



Figure 3. Daily variation in the number of people in ICU for COVID-19 (y-axis: Variation des cas en réanimation).
Source: Pandémie de Covid-19 en France, Wikipedia.



Figure 4. Daily number of COVID-19 patients in ICU units (y-axis: Personnes en réanimation).
Source: Pandémie de Covid-19 en France, Wikipedia.


Asymptomatic infections go unnoticed; even mild to moderate symptoms may go unnoticed; deaths do not. Consequently, deaths reflect the reality of the COVID-19 epidemic better than the number of SARS-CoV-2-infected people. They will, however, only provide a picture of the number of infections that have occurred 2-4 weeks before (given the median incubation period and the period of hospitalization).

However, the current numbers of COVID-19 deaths are incomplete and will soon need to be corrected upwards. (By 10%, 30%, 50% or more? Nobody knows yet.) In Italy, especially in the most hit Northern regions, a certain number of people died at home and did not appear in the official reports. Data about overall mortality in epidemic hot spots in Northen Italy (ISS 2020) and in Spain (Madrid) suggests that excess mortality due to COVID-19 might be twice the officially reported figure. In France and the UK, as in other countries, deaths from long-term care facilities were initially not included in the official data. Figure 2 shows that the number of daily deaths decreases about three weeks after the implementation of lockdown measures (Italy: 8/10 March; Spain: 14 March).


Figure 5. Daily confirmed COVID-19 deaths, rolling 3-day average. Source: www.ourworldindata.org


The data from Europe show that lockdown measures were effective but less so than in China, probably reflecting a less strict lockdown in Europe. Daily updates are available from www.ourworldindata.org (Figure 5).

To calculate  COVID-19 excess  mortality  over  1  year,  based  on  age,  sex,  and  underlying  condition-specific estimates, an online  tool is now available (OurRisk.CoV). For the UK, 293,991 deaths would be expected in a “do-nothing scenario”. With mitigation (i.e., less rigorous and voluntary measures), authors predicted between 18,000 and 37,000 deaths (Banerjee 2020).

Special Aspects of the Pandemic

The COVID-19 pandemic has highlighted a number of specific aspects and lessons learned that should be kept in mind during the management of future pandemics (by coronaviruses, influenza viruses or by as yet unknown viruses):

  • First outbreak (China)
  • Surprise or unpreparedness (Italy)
  • Unwillingness to prepare (UK, USA, Brazil)
  • Partial preparedness (France)
  • Preparedness (Germany)
  • Herd immunity (Sweden)
  • Deferred beginning (South America)
  • Splendid isolation (New Zealand, Australia)
  • Unknown outcome (Africa)

First outbreak (China)

China was caught by surprise of the COVID-19 outbreak – as any other nation would have been – but “thanks” to the SARS outbreak in 2003 (Kamps-Hoffmann 2003), was prepared for it. At first, the epidemic spread within Wuhan and Hubei Province (December 2019) and then nationwide to all provinces in January 2020, favored by travelers departing from Wuhan before the Chinese Spring Festival (Zhong 2020, Jia JS 2020). However, within 3 weeks from the identification of the identification of a new virus, the government ordered the lockdown of more than 50 million in Wuhan and the surronding province Hubei as well as travel restrictions for hundreds of millions of Chinese citizens. This astonishing first in human history achieved what even specialists didn’t dare dream: curbing an epidemic caused by a highly contagious virus (Lau 2020).

As early as four weeks after the Wuhan lockdown, there was evidence that strict containment measures were capable of curbing a SARS-CoV-2 epidemic as demonstrated in Figure 1 (page 38). The lesson from China: it is possible to lockdown entire provinces or countries and lockdown works. Some authorities in the Western Hemisphere followed the example of China (Italy, for example, ordered a lockdown as early as 18 days after the diagnosis of the first autoctonous case), other governments didn’t.

Preparedness (Taiwan)

On 7 June, Taiwan (24 million people with a population density of 650/km2), had reported 443 cases and 7  deaths. Most SARS-CoV-2 infections were not autochthonous. As of 6 April 2020, 321 cases were imported by Taiwanese citizens who had travelled once or more to 37 countries for tourism, business, work, or study (Liu JY 2020). From the beginning, Taiwan drew on its SARS experience to focus on protecting health care worker safety and strengthening the pandemic response (Schwartz 2020 + The Guardian, 13 March 2020). An early study suggested that identifying and isolating symptomatic patients alone might not suffice to contain the epidemic and recommended more generalized measures such as social distancing (Cheng HY 2020). Big data analytics were used in containing the epidemic. On one occasion, authorities offered self-monitoring and self-quarantine to 627,386 persons who potentially had contact with the more than 3000 passengers of a cruise ship. These passengers had disembarked at Keelung Harbor in Taiwan for a 1-day tour five days before the COVID-19 outbreak on the Diamond Princess cruise ship on February 5, 2020 (Chen CM 2020).

At the time of this writing, Taiwan is definitely one of the countries with the most successful management of COVID-19.

Surprise or unpreparedness (Italy)

Italy was the first European country struck by the pandemic. Complete genome analysis of SARS-CoV-2 isolates suggests that the virus was introduced on multiple occasions (Giovanetti 2020). Although the first local case was diagnosed only on 20 January, the force of the outbreak also suggests that the virus had been circulating for weeks, possibly as early as 1 January (Cereda 2020).

However, it was not straightforward to decipher the subtle signs of coming events. During the yearly flu season, COVID-19 deaths in elderly people could easily be interpreted as flu deaths. On the other end of the age spectrum, among the most active social age group – young people crowded in bars, restaurants and discos –, the rapid SARS-CoV-2 virus would not have caused life-threatening symptoms. Before being detected, the epidemic had time (at least a month) to grow.

There is one additional possible reason for the delay in recognizing the encroaching epidemic in Italy that is worth mentioning: the Italian ‘suspected case definition for COVID-19’. It included (like the suspected case definitions recommended at that time by WHO) the mandatory epidemiological criteria of ‘history of travel to  China or in contact with a person from China’ before requesting a PCR test. A strict application of this case definition discouraged testing suspected pneumonia cases where the link with China was not clear (which would eventually happen everywhere after the first asymptomatic individuals had spread the infection). The anesthesiologist who eventually requested the PCR test for Italian patient #1, Mattia, did it “under her own responsibility and not in line with MOH guidelines”.

It is as yet unclear why the epidemic took such a dramatic turn in the northern part of Italy, especially in Lombardy (Gedi Visual 2020), while other areas, especially the southern provinces, were relative spared. Of note, healthcare in Italy is run by the regions and for a long time, the Lombardy Region has favored the development of a mostly private and hospital-centered system, with great facilities but poor community-based services. This meant that patients were quickly run to the hospital, even those with minor symptoms, resulting in overcrowded emergency services and major nosocomial spread. A more decentralized and community-based system like in the Veneto Region (plus maybe a bit of luck) could have greatly reduced the mortality from COVID-19 in Lombardy. In addition, Italy had not updated nor implemented the 2006 national pandemic preparedness plan (https://www.saluteinternazionale.info/2020/04/cera-una-volta-il-piano-pandemico). The lack of preparedness and the overlap of responsibilities hampered considerably the initial coordination of the national response between the regions and the central government.

Unwillingness to prepare/denial (UK, USA, Brazil)

In the UK, clumsy political maneuvering delayed the start of effective lockdown measures by a week or more. As the epidemic doubles in size about every 7 days (Li 2020), around 50% and 75% of all deaths might have been prevented had lockdown or social distancing measures been ordered one or two weeks earlier, respectively. Early data from Ireland and the United Kingdom seem to confirm this assumption.

Like in Iran, where the regime covered up news of the coronavirus for three days to avoid impacting turnout at parliamentary elections on 21 February, domestic politics (or paranoia; BMJ, 6 March 2020) influenced the epidemic response in the United States of America. Scientific advice from CDC and other national public health institution was ignored (The Lancet 2020). The US is now the country with the highest number of cases and deaths (2 million and more than 110,000 on 7 June, respectively). Without this unprecedented vacuum in leadership in US, most of these deaths would have been prevented.

Brazil, which is also not an example of good governance performance, is on track to be the country with the second highest number of deaths.

Partial preparedness (France)

France was partially prepared, partially not. During the first national outbreak near Mulhouse, hospitals were overwhelmed. Despite the updated and well structured pandemic plan (https://www.gouvernement.fr/risques/plan-pandemie-grippale), all over the country protective equipment was in short supply; in particular, face masks were sorely lacking after a decision of the Hollande government to greatly reduce the  expensive stocks of 1.7 billion protective masks (surgical and FFP2) available in 2009 to 145 million surgical masks in 2020 (“We are not going to manage mask stocks, it is expensive, because we have to destroy them every five years. Nous n’allons pas gérer des stocks de masques, c’est coûteux, parce qu’il faut les détruire tous les cinq ans.”)  (Le Monde 200506).

However, France, thanks to Italy, had an important advantage: time. It had several weeks to learn from the events in Lombardy. When, on the weekend of 21 March, virtually from one day to the next, patients were pouring into the hospitals of the Greater Paris Region, the number of available intensive care unit beds had already increased from 1,400 to 2,000 during the preceding week. Furthermore, two years before, in a simulation of a major terrorist attack, France had tested the use of a high-speed TGV train for transporting casualties. At the height of the COVID epidemic, more than 500 patients were evacuated from epidemic hotspots like Alsace and the Greater Paris area to regions with fewer COVID-19 cases. Specially adapted high-speed trains as well as aircraft were employed, transporting patients as far away as Brittany and the Bordeaux area in the South-West, 600 km from Paris and 1000 km from Mulhouse. The French management of ICU beds was a huge logistical success.

Good virologists, huge lab network, family doctors (Germany)

Germany’s fatality rate is lower than in other countries. 7It is assumed that the main reason for this difference is simply testing. While other countries were conducting a limited number of tests of older patients with severe cases of the virus, Germany was doing many more tests that included milder cases in younger people (Stafford 2020). The more people with no or mild symptoms you test, the lower the fatality rate. Reliable PCR methods had been developed by the end of January from the Drosten group at Berlin’s Charité (Corman 2020).

Furthermore, in Germany’s public health system, SARS-CoV-2 testing is not restricted to a central laboratory as in many other nations but can be conducted at quality-controlled laboratories throughout the country. Within a few weeks, overall capacity reached half a million PCR tests a week. The same low fatality rate is seen in South Korea, another country with high testing rates.

Finally, another important reason for the low mortality in Germany might be age distribution. During the first weeks of the epidemic, most people became infected during carnival sessions or ski holidays. The majority were younger than 50 years of age. Mortality in this age group is markedly lower than in older people.

Herd immunity (Sweden)

Sweden has never really imposed a lockdown, counting on the population to adopt individual social distancing and other protective measures to curb the transmission of SARS-CoV-2. As a result, Sweden has today (7 June 2020) a death rate of 461 per million population which compares unfavorably with Denmark (101) and Norway (44), with most deaths occurring in care homes and immigrant communities. Surprisingly, an initial antibody survey in Stokholm found that only about 7% of residents had been infected with SARS-COV-2 at the end of April. Still worse, Sweden didn’t benefit economically of its no-lockdown approach as its economical performance seems to contract at a similar rate as countries in the rest of Europe (Financial Times, 10 May 2020).

For a detailed discussion of herd immunity, see Randolph 2020.

Deferred beginning (South America)

In the initial months of 2020, the number of cases were comparatively low in South America (Haider 2020). As a matter of fact, the local epidemics took off roughly 4 weeks later than in Europe (see www.worldometers.info/coronavirus). Whether this delay is due only to a deferred import of SARS-CoV-2 from the initial outbreak region in China or to other factors (sunshine intensity? Guasp 2020) is unknown. However, according to WHO, South America has not become the new epicenter of the coronavirus pandemic, with Brazil (374,000 cases and more than 23,000 deaths as of 27 May) reporting more cases than any other country in South America.

Splendid isolation (New Zealand, Australia)

With 102 deaths in Australia, 21 in New Zealand and no deaths in French Polynesia, Fiji, New Caledonia and Papua New Guinea, Oceania is the least hit area in the world. The geographical isolation may allow these countries to become the first non-COVID zones in the world. International travel to New Zealand and Australia is still banned and may be subject to quarantine measures for quite a time.

The unknown outcome

The transmissibility of SARS-CoV-2, combined with the scarcity of crucial health equipment and facilities and the challenges of implementing widespread case isolation (Wells 2020), was supposed to have a devastating impact on African countries. Until now, these predictions have not come true. Although a few hundred deaths have been reported from a small number of countries (<10), the African COVID-19 epidemic is in no way comparable to the situation in Asia, Europe and the Americas.

However, caution should be used before hypothesizing an “African exception” due to factors such as demographics (huge young populations) or previous ‘exposure to more and different pathogens’. Some official figures may be underestimates, voluntary or not, due to regional difficulties in reporting. In some cities, such as Kano, Nigeria, major outbreaks may already be under way. The New York Times reported on 17 May, “so many doctors and nurses have been infected with SARS-CoV-2 that few hospitals are now accepting patients”. Gravediggers would be working overtime. In Mogadishu, Somalia, officials say burials had tripled, according to the same report. In Tanzania, the US embassy has warned of the risk of “exponential growth” of COVID-19 cases in the country, adding that hospitals were “overwhelmed” (The Guardian, 19 May).

It is too soon to say, how COVID-19 will evolve in Africa. As the situation in South America illustrates, on the scale of continents, the pandemic can “be late” by some weeks or months and still hit very hard.

Lockdown Exit

In the next months, all countries will have to find a balance between a maximum of economic activity and a still manageable number of patients in ICUs. Lockdown exit strategies should always include

  • Strengthening of the national testing capacities to ensure access to PCR to all those in need;
  • Effective contact-tracing system;
  • Isolation capacities for positive people and close contacts.

Not all countries are able to fulfill these essential requirements, raising concerns about the possibility of new clusters and outbreaks. To facilitate identifying contacts at risk, several countries are considering developing smartphone applications that would record when other phones are coming into close contact and send an alert message in case one of these would have tested positive. However, opinions are still divided between centralized systems, where individual data would be stored in a central government server, and a decentralized system, where data will be stored in the mobile phone only. No common system has been agreed upon and the feasibility and usefulness of these apps still needs to be proven.

At the beginning of June 2020, most countries had started normalizing and restoring economic and societal activities. European borders will open again and tourism is expected to take off, albeight at a much reduced level (–50%?) compared to previous years.

Austria and Germany have eased lockdown measures for around 6 weeks, and apart from a few clusters in Germany, there is currently no indication of an imminent second “cataclysmic wave of contagion”, as the authors feared in previous editions. Italy started “Phase 2” on 4 May, with four million people returning to their workplaces, shops opening and relaxed restriction on the movements of people, including visiting relatives. The number of new cases and deaths continues to decline everywhere except in Lombardy. However, schools will remain closed until September. Spain also slightly relaxed the lockdown measures on 2-4 May allowing greater movements and outdoor sport activities. France partially ended the lockdown on 11 May, with the country divided in a “red zone” where stricter restrictions will still apply, and “green zones” where they will be gradually relaxed.

In the USA, states have set their own timetables for imposing and easing lockdown measures, with a general trend in resuming activities despite the ongoing spread of the virus and high mortality from COVID-19. The government of the United Kingdom, the latecomer in European lockdown, announced the easing of the measures for 15 June.

Sweden has never really imposed a lockdown, counting on the population to adopt individually social distancing and other protective measures. Given the observed high death rate compared to neighbouring countries, there is now public pressure to implement stricter lockdown measures.

In all countries, most activities will eventually resume, but the tight-rope walk between maximising economic output and avoiding a new COVID-19 outbreak will need careful evaluation and considerations would include:

  • Recommend frequent handwashing, disinfection, distancing (shops) and face masks (transport and other public places);
  • Order distancing in cinemas, theaters and operas, and consider preventive contact tracing schemes in case an attendent should later be found to be infected;
  • Ban events and activities that put people at less than one meter of distance (sports events, concerts, disco, festivals, pubs, etc.);
  • Implement mandatory requirements of wearing face masks in public (Anfinrud 2020);
  • In the case of local outbreaks, recommend limitation in the movement of people and consider applying special restrictions to population groups at higher risk (e.g., elderly people, people with health conditions that put them at risk of severe COVID-19).

Some activities might remain closed for an unknown period of time, possibly until the availability of a vaccine.

In some countries, including the US, the epidemic is far from over with many new cases and deaths being reported every day. Therefore, it looks like the decision to exit the lockdown is more driven by economic necessity than justified by a satisfactory epidemiological situation. In this “second half” of the match “COVID vs. Humanity”, the economists are coming back and scoring more goals that the public health officials.

The economic impact of the COVID-19 pandemic is certainly unprecedented. The International Monetary Fund (IMF) forecasts a contraction of 3% of the planet’s GDP in 2020. In a recession like no other in peacetime for nearly a century, the countries of the Euro zone, the United States and the United Kingdom might see a contraction in activity of between 5.9% and 7.5%[1]. Economically, socially, and politically, protracted lockdown is unsustainable. What can be done once – self-isolation of the population for months and months – can probably not be repeated.

“COVID Pass”

In countries with large COVID-19 outbreaks, tens of thousands of people died. Those who survive severe or less severe illness, with or without hospitalization, will have developed antibodies against the SARS-CoV-2 virus (Zhang 2020, Okba 2020). Even more people, those who were infected but developed no symptoms, will have antibodies, too. Already, millions of people in China, Italy, Spain, France, and the US have developed SARS-CoV-2 antibodies.

In early June 2020, we still cannot be sure if and for how long these antibodies protect against a second infection. On 24 April, WHO issued a Scientific Brief stating that “There is no evidence yet that people who have had COVID-19 will not get a second infection” (WHO 200424). However, recently, neutralizing antibodies against SARS-CoV-2 were detected in virtually all hospital staff sampled from 13 days after the onset of COVID-19 symptoms (n=160) (Fafi-Kremer 2020; see Le Monde, 27 May) and there is no reason why they should not, since even symptomatic people recover from the infection, and most researchers think, based on our general knowledge of coronavirus infection, that neutralizing antibodies are likely to be protective. Though further studies are needed to support this, it is very likely that once people have recovered from SARS-CoV-2 infection, they would not be vulnerable to a secondary infection and, even if they had a mild infection, they would be unlikely to infect others.

This has led to speculations about the possible introduction of a SARS-CoV-2 antibody passport, or a COVID Pass. People with neutralizing antibodies – assumed to be protected following a symptomatic or asymptomatic COVID-19 infection and therefore unable to transmit the virus – would be allowed to freely move around. Chile, Germany, and the UK, among others, considered implementing certifications that a person has contracted and recovered from COVID-19. These “licenses” would then allow immune people to engage in economic activity and provide safer care for vulnerable populations. The intention was to develop population-level ‘shield immunity’ by amplifying the proportion of interactions with recovered individuals relative to those of individuals of unknown status (Weitz 2020).

Major concerns remain as community licensing could stigmatize people, undermining the value of equal treatment. Immunity-based licenses would require therefore careful implementation to be ethical in practice (Persad 2020) and there are at least 10 good reasons why COVID (or immunity) passes are a bad idea (Kofler 2020), foremost because restricting liberty on the basis of biology threatens freedom, fairness and public health.

For the time being, a confirmed positive SARS-CoV-2 serological positivity might be useful in health care settings to determine who, among the health workers, should be allowed to work in close contact with confirmed or suspected COVID-19 patients.

The second wave

For now, in June 2020, the second wave of the COVID pandemic, as hypothesized in a study by Ferguson (Ferguson 2020; figure 7) has not yet materialized. The study predicted that for as long as most people had no immunity against SARS-CoV-2, the lifting of strict “Stay at home” measures such as extreme social distancing and home quarantines would inevitably make the epidemic bounce back.


Figure 7. Impact of non-pharmaceutical interventions (NPIs) to reduce COVID-19 mortality and healthcare demand (Source: Ferguson 2020).


However, the world has changed. Today, a fever, a cough, anosmia and many other more subtle COVID symptoms will usually trigger an immediate cascade of action to prove or refute an acute SARS-CoV-2 infection. An existing acute infection, for its part, will trigger a similarly immediate cascade of contact tracing, testing, and quarantining. In addition, many people, while waiting for the coming episodes of the pandemic to unfold, have changed their behavior and avoid mass gatherings. They have understood that restrictive social-distancing measures will need to be combined with widespread testing and contact tracing to end the ongoing pandemic (Giordano 2020 + less realistic, Peto 2020).

Herd immunity, the notion introduced to a wider public by a foolish politician, will not not be on the agenda for a long time. As for now, not a single country is anywhere close to reaching herd immunity. Even in past hotspots like Wuhan, the prevalence of SARS-CoV-2 IgG positivity was 9.6% among 1,021 people applying for a permission (the SARS‐CoV‐2 nucleic acid test needed to be negative) (Wu X 2020). A French study projected 2.8 million or 4.4% (range: 2.8–7.2) prevalence of infections in France. In Los Angeles, the prevalence of antibodies was 4.65% (Sood 2020). (And even this low number may be biased because symptomatic persons may have been more likely to participate.) A recent nationwide coronavirus antibody study In Spain showed that about 5% of the population had contracted the virus. These infection rates are clearly insufficient to avoid a second wave of a SARS-CoV-2 epidemic (Salje 2020).

Coronaviruses have come a long way (Weiss 2020) and will stay with us for a long time. Questions abound: When will we move freely around the world as we did before? How many years will air traffic need to return to pre-COVID-19 levels? Will we be inclined to plan vacations nearer to home than at the other side of the globe? Will we wear face masks for years? Will there be any nightlife event with densely packed people dancing and shouting and drinking in any city of the world anytime soon?

The French have an exquisitely precise formula to express unwillingness for living in a world you do not recognize: “Un monde de con!” Fortunately, we will be able to walk out of this monde de con thanks to a scientific community which is larger, stronger, and faster than at any time in history. (BTW, should politicians who are skeptical of science be ousted out of office? Yes, please! It is about time now!) As of today, we do not know how long lasting, how intense, and how deadly this pandemic will be. We are walking on moving ground and, in the coming months, we will need to be flexible, resilient, and inventive, looking for and finding solutions nobody would have imagined just months ago. Sure enough, though, science will lead the way out. If we could leap three years into the future and read the story of COVID-19, we would not believe our eyes.


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[1] The global CO2 emissions decreased by 17% by early April 2020 compared with the mean 2019 levels, just under half from changes in surface transport (cars, truck, buses) (Le Quéré 2020). More than one billion tons of carbon emissions less. At their peak, emissions in individual countries decreased by an average of 26%, admittedly extreme and probably unseen before, but just to the level of emissions in 2006. The impact on 2020 annual emissions will depend on the duration of the confinement, with a low estimate of –4% if pre-pandemic conditions return by mid-June, and a high estimate of –7% if some restrictions remain worldwide until the end of 2020. These figures are comparable to the rates of decrease needed year-on-year over the next decades to limit climate change to a 1.5°C warming.