COVID-19: How long does one stay immune after being infected?

The issue of the duration of immunity after Covid-19 infection is central to all levels. According to a Chinese study, it could be short-lived, especially in asymptomatic patients.

Among the major questions that persist on Covid-19, that of immunity is particularly difficult: today, there is still no certainty on the nature or duration of the potential immunity generated by a Covid-infection. 19. Today, two studies published in Nature and medRxiv reveal that the antibodies could disappear after two to three months in infected people, but asymptomatic. These patients may therefore not have any long-term immunity to Covid-19.

The researchers therefore analyzed the levels of antibodies present in patients. These small proteins, which are the basis of the body’s immune defenses, act as a witness: if found in significant quantities, this means that the mechanisms of immunity have started to work. According to the study, almost 10% of the 1,500 patients tested had undetectable antibody levels “a few weeks” after infection, a figure that rises to 74% two to three months after infection. This is much shorter than previous coronaviruses like SARS or MERS, for which the antibodies had a lifespan in the order of a year. In addition, this finding would particularly concern asymptomatic people according to the second study: the antibody level would have dropped by 81% after two months in patients without symptoms, against 62% for symptomatic patients. Obviously, these conclusions require more data to be confirmed, in particular those of the second study carried out on a much smaller number of individuals. But both of them corroborate in any case other work which already suggested a short lifespan of the antibodies and it would seem that this is indeed limited to a few months, even weeks in some cases.

Duration of immunity, a key factor in the control strategy

The ideal would be to be able to confirm or deny this finding quickly, since questions of the duration and nature of immunity are fundamental to establishing a long-term control strategy. Rest assured, this does not call into question the fact of being able to develop a vaccine since we already have proof that immunity is possible. On the other hand, if the natural immunity generated by the virus proves insufficient to prevent its large-scale transmission, this means that there is an urgent need for a powerful vaccine, on pain of never being able to reach the famous group immunity . The challenge will be to successfully develop a vaccine capable of generating longer immunity in the shortest possible time. A complicated task, according to Anthony Fauci, director of the National Institute of Allergies and Infectious Diseases in the United States, who recently explained that the lack of consistency in the methodology of the various studies slowed down the process. In addition, it appears that different individuals exhibit “no uniformly robust response” to infection, another obstacle to the development of a large-scale vaccine.

But it is also the whole strategy of social distancing that could be called into question and require a thorough overhaul. By developing weaker immunity, asymptomatic patients could be more important vectors than previously envisaged. Our current screening strategy may therefore be behind schedule, as these asymptomatic, but nonetheless infected patients could be identified as healthy in the absence of antibodies. Pending more details on the exact duration of immunity, the conclusion to be drawn is very clear: continue to apply the rules of social distancing!

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