More than four million French people have received a first dose of the AstraZeneca anti-covid vaccine. But what is the instruction for the second dose? Because since March 19, the French health authorities have restricted the use of this vaccine to over 55s, an age group where the benefit of being vaccinated is very high and where the risk of atypical thrombosis is greatly reduced.

A position that the Haute Autorité de Santé (HAS) has still confirmed on May 12 : the AstraZeneca vaccine (renamed Vaxzevria®) should not be administered to people under 55 years of age, even if they sign a discharge, as is the case for example in Germany.

If you are over 55

If you have already received a dose of AstraZeneca and you are over 55 years old, the HAS recommends that you be vaccinated with this same vaccine for the second dose. “You must absolutely be vaccinated with AstraZeneca when you are over 55 years old“affirmed Prime Minister Jean Castex to the JT of France 2 on May 11.

In its press briefing of May 11, the Ministry of Health was even stricter: “People over 55 who have had AstraZeneca will not be able to change their vaccine for the second injection. There is no reason to change and healthcare professionals need to stand up. This protocol must be respected. “

The time between the two doses must be 12 weeks and the vaccination can be carried out in a vaccination center but also in a pharmacy, in a nursing office or at a general practitioner, specialist or occupational physician.

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If you are under 55

You received your first dose of AstraZeneca vaccine before March 19, but you are under 55 years old. In this case, the HAS has recommended since April 9 to inject 12 weeks after the first dose a second dose of a messenger RNA vaccine : Pfizer or Moderna.

This is what scientists call the “heterologous prime-boost” strategy. “A two-step vaccination scheme using for the second injection (boost) a vaccine using a technique different from the first (prime) “ defines the HAS in a press release April 9.

This strategy is opposed to that of “homologous prime-boost” for which the first injection and the booster are carried out with a vaccine using the same technique, messenger RNA or adenovirus.

Effective against variants?

If other variants of the coronavirus were to emerge, the question of the vaccine booster with another vaccine, even in those over 55 years old, would arise, breathed on May 10 the Minister of Health Olivier Véran on the plateau of LCI.

The “heterologous prime-boost” strategy could then also be implemented in those over 55 who have already received two doses of AstraZeneca. They would then receive a booster with a vaccine based on another technique, for example that of messenger RNA.

A “heterologous prime-boost” for all?

And this strategy could even become generalized because it “has been shown to be more effective than the homologous prime-boost approach in phase 1 and 2 studies in humans“underlines the HAS.

According to this authority, “many studies in progress“and” lhe first data on the use of heterologous prime-boost in anti-SARS-CoV-2 vaccination“are certainly”still limited “ But “encouraging“.

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What about AstraZeneca stocks?

The controversy around AstraZeneca has caused a delay in vaccination with this vaccine. As a result, France would have more than three million doses in reserve, already delivered or ordered and awaiting delivery. But only 20,000 AstraZeneca first-time injections are performed on average per day, according to figures from CovidTracker.