Recent scientific work shows that people who have been infected with SARS-CoV-2 have acquired immunity which lasts for at least nine months.
In other words, for a relatively long period of time, we can’t become ill with COVID-19 twice. This important and most welcome news will have significant consequences.
According to official statistics on November 27:
- 61.36 million people worldwide have been infected with the coronavirus, of which
- 17.48 million (28.49%) are still visibly ill
- 1.44 million (2.35%) have died
- 42.44 million (69.16%) are cured definitively, or at least for a reasonably long period.
The worldwide recovery total includes the following national figures:
- India: 8,718,517
- US: 7,849,718
- Brazil: 5,528,599
- Russia: 1,712,174
- Germany: 676,100
- Italy: 661,180
- Poland: 494,869
- Canada: 280,923
- Switzerland: 218,900
- France: 158,236
- Japan: 116,378
- Belgium: 36,912
The above figures underestimate the real totals considerably. Since the start of the pandemic, the number of people cured is calculated using only diagnosed cases. But cases for which there have been positive tests are only a part of the real number of cases.
Millions of people have been in contact with coronavirus without being tested or even without realising it. Most of them have recovered, or will recover, without having been counted in any way. Figures for France are particularly understated because of a strict method of counting cases but insufficient follow-up due to lack of testing capacity.
Scientists have needed to be convinced of the reality of lasting immunity. A significant change in position is taking place.
- The World Health Organisation (WHO) said on April 24: "No study has evaluated whether the presence of antibodies to SARS-CoV-2 confers immunity to subsequent infection by this virus in humans," using this as a counter-argument against the idea of an immunity passport. "At this point in the pandemic, there is not enough evidence about the effectiveness of antibody-mediated immunity to guarantee the accuracy of an 'immunity passport'."
- On November 25, Nigel McMillan director of infectious diseases and immunology at the Menzies Health Institute, Griffith University in Australia summarises the latest research in The Conversation: "New research suggests immunity to COVID is better than we first thought. Latest research suggests key parts of the immune system can remember SARS-CoV-2 for at least eight or nine months, and possibly for years."
"There have been just 26 confirmed cases of reinfection reported worldwide so far. With 60 million people infected globally so far, reinfection therefore seems to be a very rare event," McMillan writes.
These extremely rare cases of reinfection are exceptions that prove the rule of immunity which applies to most illnesses, including viral ones. Some cases of “reinfection” in April in South Korea have been shown to be diagnostic errors. Fragments of dead virus were mistaken for the virus itself.
More recently, it has been noticed that numerous commercial tests don’t detect the antibodies which are most effective in overcoming the virus. The quantity of these antibodies tends to diminish and they become hard to detect a few months after a first infection. We know now that, in case of a new attack, the organism is always ready to produce enough antibodies to avoid a second infection.
Further, it’s not just antibodies which contribute to immunity. "A small number of people may not produce any antibodies to the coronavirus. But even in that unlikely event, they will have so-called cellular immunity, which includes T cells that learn to identify and destroy the virus. Virtually everyone infected with the coronavirus seems to develop T-cell responses, according to several recent studies."
These T cells bind directly to infected human cells within the body and destroy them. Earlier this month, researchers from China and Germany showed that T cell memory responses were still present nine months after infection. They studied patients from Wuhan, where the first reported COVID cases occurred, and who therefore have the oldest immune responses. So, people who’ve been naturally infected with SARS-CoV-2 should be protected for at least nine months after their first infection.
The certainty of lasting immunity constitutes great progress in our knowledge of COVID-19 in pathological and epidemiological terms. This improved knowledge should help us to better manage the crisis in its economic and social dimension as well as in terms of health.
As we are now in the process of examining the effectiveness and the possibility of side-effects of the COVID-19 vaccinations which will be administered to entire populations in coming months, it’s reassuring to know that tens of millions of people already have lasting natural immunity and that their number will continue to increase as SARS-CoV-2 keeps circulating.
The public authorities should take full advantage of this lasting immunity. Possible steps include:
1- Defining appropriate status for those who are cured.
2- Adjusting deconfinement rules to take account of the immune status of those who are cured, and who present no further risk to themselves or others.
3- Adapting coming vaccination campaigns to take account of the immune status of those who have recovered.
4- In case of doubt on the effectiveness of coming vaccinations, the immune status of vaccinated people should be compared with that of those who were ill and have recovered using a serological test showing the presence of antibodies. A certificate of vaccination against COVID-19 can be reinforced by a serological test showing the presence of antibodies, as would be needed for an immunity passport.
5. Relaunch the plan for an immunity passport which has been hampered by doubts - now lifted - on the persistence of antibodies and length of immunity acquired.