Covid-19: why have some people vaccinated against the virus developed serious forms of the disease?

the essential
An international study looked at the rare cases of people who were vaccinated against SARS-CoV-2 and who developed a severe form of the disease. In some of these patients, immune failure was observed.

This is undoubtedly the main objective of the vaccination campaigns which are today carried out against Covid-19: to protect against serious forms of the disease. During this pandemic, some people who completed their vaccination schedule unfortunately suffered an immune deficiency. How is it possible ?

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An international study, published last June, asks the question. Published in the journal Science Immunology and led by a French team of researchers, this study looked closely at 48 cases of severe forms of the disease in people who had completed their vaccination schedule. Inserm, Paris Cité University and the Imagine Institute have recruited patients from Greece, France, Turkey, Macedonia, Ukraine and the United States. There are 34 men and 14 women here, aged 20 to 86. The latter, all vaccinated against the virus, were infected with the Delta variant of Covid-19. All were also admitted to intensive care following their infection.

The autoantibody trail

To understand how these patients developed a severe form of the disease, the researchers first wanted to know if the vaccine had allowed these people to elicit an immune reaction. The objective: to ensure that the vaccine had worked correctly in these patients. Six patients were excluded from this study and for good reason: the vaccination had not made it possible to provide them with neutralizing antibodies.

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In the remaining 42 patients, however, the researchers found an antibody that targets certain molecules of our immune system: “type 1 interferons” (IFN-1). It is these antibodies which are responsible for fighting against the virus and which make it possible to stop its replication. 10 of the 42 patients who were examined actually developed “auto-antibodies” that prevent IFN-1 from working properly. These autoantibodies were present in these patients long before they were infected with the virus.

“Because of these auto-antibodies, these patients cannot oppose SARS-CoV-2 with a rapid line of defense via interferons, explains Paul Bastard, one of the signatories of the study, to our colleagues from the World. Lacking this first defense, the virus multiplies too quickly. The anti-Covid-19 antibodies induced by vaccination arrive too late: they fail to neutralize the virus.” Paul Bastard believes that it would be useful to track down these “auto-antibodies” in immunocompromised people: “The percentage of people with these autoantibodies increases a lot with age: less than 1% among those under 65, it exceeds 4% among 80-85 year olds”, concludes the researcher.

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