Antibodies, antigens, reinfection… The vocabulary of immunity has entered everyday language because of the pandemic. But in a year and a half of the crisis, knowledge about the immune reaction to Covid-19 has evolved and will probably continue to improve in the months to come. A recent Strasbourg study found antibodies in the blood of patients up to thirteen months after infection, but sowed the seeds by evoking the ability of the South African variant, for example, to bypass the immune system.
For Release, Brigitte Autran, expert in immunology and head of the monoclonal antibodies group at the new Agency for Emerging Infectious Diseases (ARNS), reviews the most recent data on acquired immunity against Covid-19.
What do we know today about immunity after a Covid-19 infection?
The immunity acquired after infection with the Sars-Cov-2 virus is similar to that obtained after other viral infections. We know that 95% to 99% of patients will develop antibodies. And the neutralizing antibodies, the ones that really attack the virus, appear after ten to fifteen days.
There is then a turning point on the fourteenth day after infection. If the patient has enough neutralizing antibodies at this time, then there is little risk of their condition getting worse.
How long does this protection last?
Several months. It is known that antibody production will peak about a month after infection. Then their presence will decrease. It is also known that the level of antibodies in the patient is correlated with the severity of the disease. Hospitalized patients have more residual antibodies than asymptomatic ones. A recent study still found antibodies up to thirteen months after infection in most of the people followed.
Is immunity also effective against variants?
Re-infections with the same variant are exceedingly rare. But there is a risk of reinfection by variants carrying the E484 mutation (Indians, Brazilians, South Africans). They have been shown in the laboratory to be able to partially escape the action of neutralizing antibodies from patients infected with the historic Wuhan lineage.
That said, observations in the general population tend to show that real immunity resists variants better than what is observed in vitro.
We tend to associate immunity with the presence or absence of antibodies, but it’s more complex than that …
Indeed, immune memory is based in part on cells, B lymphocytes, capable of producing antibodies. Furthermore, the immune response also has a cellular component which depends on T lymphocytes, in particular CD4 cells known to be the targets of the AIDS virus, the action of which is not taken into account by these studies on antibodies.
Should people who are immunized by a natural infection be vaccinated?
Yes, but one dose is enough. Performing this injection is important because it will significantly increase the antibody level. On the other hand, it is recommended to wait three months to carry out it in order to prevent the antibodies present after the disease from blocking the vaccine.