Covid-19: a single dose of Pfizer is less likely against certain variants, according to a study

After a single dose of Pfizer vaccine against Covid-19, we are less likely to produce protective antibodies against the variants initially detected in India and South Africa than against that initially spotted in England, according to a laboratory study published on Friday. .

“Although these kinds of laboratory results are useful (…), antibody levels alone are not sufficient to determine the level of effectiveness of vaccines, and real population studies should also be carried out”, nuance, however, in a press release from the Francis Crick Institute in London, which carried out this work with the British National Institute for Health Research (NIHR).

Published in the medical journal The Lancet, the study evaluates the production of protective antibodies (called “neutralizers”) of people vaccinated with Pfizer / BioNTech.

For this, the researchers put the blood samples of these people in the presence of several strains of the virus: its first versions (the one discovered in Wuhan in China and the one which dominated in Europe in the aftermath), the Alpha variant (nicknamed English variant ), the Beta variant (initially detected in South Africa) and the Delta variant (initially detected in India).

Dose of Pfizer-BioNTech vaccine prepared for the population of Cyprus in May 2021 (AFP / Archives – Amir MAKAR)

“After a single dose of Pfizer / BioNTech, 79% of people had a detectable antibody response against the original strain, but this dropped to 50% for the Alpha variant, 32% for the Delta variant and 25% for the Beta variant,” according to the Francis Crick Institute.

“The key is to ensure that vaccine protection remains sufficient to prevent as many people as possible from hospitalization. Our results suggest that the best way to do this is to quickly administer the second dose of vaccine,” he said. commented one of the researchers, Emma Wall, quoted in the press release.

In late May, to stem the spread of the Delta variant in the UK, the interval between two doses of vaccine (up to three months) was reduced to eight weeks for people over 50 and the most vulnerable. The results published Friday “confirm” this decision, according to the Francis Crick Institute.

In France, the government has just announced that this spacing could be exceptionally modified this summer, to prevent the second dose from falling during the vacations of the vaccinated.

So far, for RNA vaccines (Pfizer and Moderna), the gap was around 6 weeks. From now on, the second injection can take place between 5 and 7 weeks after the first.

In addition, the study published in The Lancet shows that after two doses of the Pfizer vaccine, the level of protective antibodies is lower in the presence of the Delta variant than of the other variants. These results corroborate those of other studies, including one from the Institut Pasteur in France.

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