Covid-19: in people already infected, immunity would be stronger and longer lasting

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How long does the immune response last after infection with Covid-19? Many studies have focused on this question. The latter indicate that the antibodies would last in time and that vaccination would strongly reinforce this immunity.

How long does this immune response last in people who have already been affected by the coronavirus? Several studies broadcast by Le Monde and The New York Times have looked at the issue and shown that it could be strong and long-lasting - immunity could persist for at least a year after infection, or even for several years.

In people who have been affected by Covid-19, "antibodies against the spike protein of the virus (anti-S) decrease more rapidly in men than in women, but persist in almost all people for up to 13 months later of the infection ", according to the press release of the university hospitals of Strasbourg.

This is the conclusion of a study published on May 15 on the scientific pre-publication site Medrxiv. To establish this observation, the researchers followed 393 hospital employees who contracted a mild form of Covid-19 for up to 422 days after the onset of symptoms. They found that one year after infection, 97% of them had retained their anti-S antibodies. They "are stable and this is very good news," said Samira Fafi-Kremer, director of the Institute of Virology in Strasbourg and co-author of the study.

The study also shows that after a dose of vaccine, the level of antibodies increases strongly "regardless of the prevalence rate and regardless of the type of vaccine administered."

Covid-19: antibodies that can persist for life?

Another study published in the journal Nature on May 24 and conducted by researchers at the Washington University School of Medicine in St. Louis (United States) makes the same observation: the immune response after Covid-19 infection would persist in time. "Months after recovering from a mild form of Covid-19, the body's immune cells continue to produce antibodies against the virus that causes this disease. These cells could persist for life, producing antibodies by permanence."

The study reveals that the level of antibodies decreases after infection with Covid-19, finally reaching a plateau. Some of these antibodies, long-lived plasma cells, then migrate to the bone marrow "where they constantly secrete low levels of antibodies into the blood to help protect against a new encounter with the virus," the press release specifies. But that's not all: the study also detected the presence of memory B cells, which also confer immunity against the virus.

However, this work underscores the interest of vaccination after a Covid-19 infection, because some of the patients followed had very low levels of antibodies. "Even if you've been infected, it doesn't mean you have an exceptional immune response," said study co-author Dr. Ali Ellebedy.

Vaccination strengthens naturally developed immunity

Memory B lymphocytes have also interested researchers at Rockefeller University (United States). In a study published May 9 in the pre-publication scientific journal Biorxiv, they followed 63 people who contracted Covid-19 in the spring of 2020. They found that the antibodies produced by memory B lymphocytes also became more effective in neutralizing Sars. - CoV-2, "suggesting that these people developed an enhanced and durable defense against the virus." Immunity can persist for up to a year after infection.

But that's not all: the researchers also found "that vaccination boosts the immunity developed naturally by these people during infection, to such an extent that they are probably protected even against emerging variants," a press release can read.

Therefore, having been infected with the virus and vaccinated against Covid-19 would confer particularly strong immunity. "It is clear that vaccination enhances antibodies and memory, so we can expect to be protected for several years," said Samira Fa-Kremer, co-author of the study published in Medrxiv.

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