3rd dose: “Should you use the same vaccine against Covid as for the previous injections?” “



Dear Anna,

The vaccines proposed for this new wave of vaccination against Covid-19 will be messenger RNA vaccines “Regardless of the vaccine used for the primary vaccination”, indicates the General Inspectorate of Health (IGS) in its note dated August 27. This third injection must therefore be done with Comirnaty from Pfizer or Spikevax from Moderna.

→ FILE. The answers to your questions about the vaccine booster

People affected by the third dose (aged at least 65 or with comorbidities and whose last injection was more than six months old) who have already received one or more doses of AstraZeneca or Janssen should therefore continue their vaccination course. with a dose of Pfizer or Moderna.

Note that people vaccinated with Janssen – for which the National Medicines Safety Agency (ANSM) reports numerous vaccine failuresmay receive their third dose only one month after their previous dose, compared to six months for other types of vaccines.

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Combining several different vaccines, is it more efficient?

Aside from mild side effects, which might be more common when different vaccines are injected, combining multiple vaccines is not dangerous, the study notes.CovCom conducted by the University of Oxford. The first results published on June 25 also show that combining two vaccines increases their effectiveness.

→ EXPLANATION. Covid-19: do vaccines have the same effectiveness for everyone?

In this strategy called “Heterologous Prime Boost”, the injection of a second vaccine different from the first “boosts” the first injection. “We stimulate the immune system differently, so the immune response is more robust”, summarizes Yannick Simonin, virologist at the University of Montpellier. This technique has already been used in particular to develop vaccines against Ebola, Hepatitis B and C or avian flu.

→ DEBATE. Covid-19, do we need a third dose of vaccine for everyone?

To date, there is no recommendation on one combination more effective than another. The CovBooth study, currently being conducted by the University of Southampton, England, is to provide information on the effect of combining a different vaccine for the third dose.

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