One dose instead of two? People who have already contracted covid may only need one shot of the vaccine instead of the regular two. This is what reveals a study posted on the pre-publication site medRxiv on February 1 by researchers at Mount Sinai Hospital in New York (United States).

10 to 20 times more antibodies

For this study, the researchers first recruited 109 people: 41 had antibodies inherited from a previous coronavirus infection and the 68 others did not. All of these volunteers received a first dose of messenger RNA vaccine (Pfizer / BioNTech or Moderna) in 2020.

They then measured the amount of antibodies in the blood, a marker of the immune response, in all of these participants. Result: the amount of antibodies after a dose of vaccine in people with pre-existing immunity is “equal or even greater “, sometimes 10 or 20 times, to those of people never infected.

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Stronger side effects

And that’s not all. The researchers also compared the side effects after a vaccine dose in 231 volunteers: 148 never infected and 83 already infected with covid. They then observed that people who had previously had covid expressed side effects – fatigue, headaches, chills, fever, muscle or joint pain – stronger and more frequent.

What does that mean ? That a single dose of vaccine provokes a very rapid immune response in people already infected in the past, interpret the authors of the study. And that the first dose of vaccine might “serve as a reminder in naturally infected people“.

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Releasing many doses

Ongoing follow-up studies will show whether these initial differences in immune responses hold up over time.“temper the researchers.

But this first study could already pave the way for policy change, “to give these people only one dose of vaccine“. That”would not negatively impact their antibody levels, save them unnecessary pain and release many urgently needed doses of vaccine“write the researchers.

But how do you safely identify people who only need one dose? By using, before vaccinating, serological tests which detect the presence of antibodies in the blood, finally propose the authors of the study.

“Be as economical as possible”

An idea that has already convinced France, as evidenced by Rémi Salomon, president of the establishment medical commission of the AP-HP (Assistance publique-Hôpitaux de Paris) at the microphone of France Info February 2: today, “we recommend to those who have already done the covid“to be injected”a single dose“, he specifies, before adding:”given the shortage (of vaccine doses, editor’s note), I think it’s important to be as economical as possible and it’s logical. “