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

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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, immunological failure was observed.

This is, without a doubt, the main objective of the vaccination campaigns that are carried out today against Covid-19: to protect against serious forms of the disease. During this pandemic, some people who completed their vaccination schedule unfortunately suffered from immune deficiency. How is it possible ?

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An international study, published last June, asks the question. published in the magazine science immunology and led by a French team of researchers, this study closely analyzed 48 cases of severe forms of the disease in people who had completed their vaccination program. 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, ages 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 after their infection.

The trail of autoantibodies

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 cause an immune reaction. The objective: to verify that the vaccine had worked correctly in these patients. Six patients were excluded from this study and for good reason: vaccination had failed to provide them with neutralizing antibodies.

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

“Because of these autoantibodies, these patients cannot oppose SARS-CoV-2 with a rapid line of defense through interferons,” explains Paul Bastard, one of the study’s signatories, to our colleagues at 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 these “autoantibodies” in immunosuppressed people: “The percentage of people with these autoantibodies increases a lot with the age: less than 1% among those under 65 years of age, it exceeds 4% among those between 80-85 years of age”, concludes the researcher.

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