Antibody-based immunity, acquired after curing Covid-19, would mostly disappear within a few months, according to a new study, which could complicate the development of an effective vaccine in the long term.
"This work confirms that protective antibody responses in people infected with SARS-CoV-2 (…) seem to be declining rapidly," said Dr Stephen Griffin, associate professor at the University of Leeds School of Medicine, on Monday. (United Kingdom). "The vaccines under development must either generate stronger and more durable protection against natural infections, or be administered regularly," added this doctor who was not involved in the study.
Antibodies scrutinized day after day
"If the infection gives you antibody levels that go down in two to three months, the vaccine will potentially do the same," and "a single injection may not be enough," says lead Dr. Katie Doores. author of the study, in the Guardian . The study from the prestigious King's College London, which has not yet been peer reviewed, has been posted on the medrxiv website.
The researchers studied the immune response in more than 90 confirmed cases (including 65 by virological tests) and show that the levels of neutralizing antibodies, capable of destroying the virus, peak on average around three weeks after the onset of symptoms, then decline rapidly. According to blood tests, even individuals with mild symptoms have had an immune response to the virus, but generally less than in more severe forms. Only 16.7% of subjects still had high levels of neutralizing antibodies 65 days after the onset of symptoms.
Other cells in play
The study also tends to undermine the policy of collective immunity, which is supposed to protect everyone, after a high percentage of the population has acquired immunity after being infected. Experts point out, however, that immunity is not just based on antibodies, the body also producing immune cells (B and T) that play a role in defense.
"Even if you end up with no detectable circulating antibodies, it doesn't necessarily mean that you don't have protective immunity because you probably have immune memory cells that can quickly go into action to start a new immune response if you experience the virus again. So you may get a milder infection, ”says professor of viral immunology Mala Maini, consultant at University College London.
Until further information is learned, "even those with a positive antibody test - especially those who cannot explain where they may have been exposed - should continue to exercise caution, social distancing and use an appropriate mask, ”warns James Gill, honorary clinical professor at Warwick Medical School.
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