everything you need to know about the third dose

The vaccine booster campaign is in full swing and when making an appointment, many of us ask ourselves the question: with which vaccine is it better to do it? In France, only RNA vaccines, from Pfizer / BioNTech and Moderna, are offered for this third dose. Is there one to favor? Moreover, not everyone has had the same primary vaccination, that is to say the sequence of the first two doses. Some have received one dose of Janssen, others two doses of AstraZeneca, Pfizer / BioNTech or Moderna… Should this be taken into account?

Let us remember to begin with that the third dose, also called a “booster” or “booster”, is now recommended for the entire adult population five months after the end of the primary vaccination (second dose). For Janssen vaccines, a second dose was added at one month, and the booster takes place, as for the others, five months later. The preservation of the sanitary pass is conditioned on it. And for good reason: the third dose is nothing superfluous or anecdotal. Without it, vaccination quickly becomes obsolete, experts insist. Studies have shown a significant drop in the protection conferred by vaccines, whatever the brand, after a few months against the risk of infection; the effect against the severe forms is maintained more, but decreases nevertheless, in particular for the oldest.

SEE AS ​​WELL – Covid: a booster dose is “safe and effective” three months after the last injection according to the EMA

Risk of death reduced by 90% in those over 50

The benefits of the third dose can now be seen in countries that started their recall campaign early, especially in Israel. A study published on December 8 in the New England Journal of Medicine , conducted on more than 840,000 Israelis first vaccinated with Pfizer / BioNTech’s Comirnaty, shows a 90% reduced risk of death in people over 50 who received a third dose after five months, compared to people vaccinated who have not received a third dose. Another study published in the Lancet on December 4, also based on Israeli data, shows that the booster, 7 days after his injection, protects 93% against the risk of hospitalization and 92% against the risk of severe form of Covid. “These are important results which confirm the interest of the third dose in a context of variant Delta responsible for the current epidemic wave», Indicates the P^r Odile Launay, coordinator of the clinical investigation center at Cochin-Port-Royal hospital (AP-HP).

Read alsoThird dose: have the vaccines been adapted to the variants?

Specialists don’t have as much “real-life” hindsight for Moderna’s vaccine, but Moderna has always presented very similar results and third-dose clinical trials have shown a dramatic rise in antibody levels. “Comirnaty from Pfizer / BioNTech or Spikevax from Moderna, it doesn’t matter», Assures the P^r Jean-Daniel Lelièvre, head of the infectious diseases department at Henri-Mondor hospital in Créteil (AP-HP) and member of the Technical Committee for Vaccination at the Haute Autorité de santé. Same mechanism of action and same levels of efficacy and safety, both can be used interchangeably as a booster.

Note, however, that those under 30 will only be offered the injection of Pfizer / BioNTech, because a slight increased risk of myocarditis or pericarditis (inflammation of the heart muscle or pericardium) has been observed in young adults with Moderna’s Spikevax. , especially in men. The risk induced by vaccination remains however very low and much lower than that generated by the Covid itself. The position of the Haute Autorité de santé is above all motivated by a form of precautionary principle and the availability of an alternative.

The order of the vaccines is important: the Pfizer-Pfizer-AstraZeneca sequence is not as interesting as AstraZeneca-AstraZeneca-Pfizer

Prof. Jean-Daniel Lelièvre, head of the infectious diseases department at Henri-Mondor hospital in Créteil (AP-HP) and member of the Technical Committee on Vaccination at the Haute Autorité de santé

Another notable fact about the Moderna booster, it is done with only half a dose. “Their serum was much more concentrated in messenger RNA than that of Pfizer, so the laboratory conducted clinical trials with a half-dose which proved to be conclusive. Rather, it is an industrial and financial issue, without affecting efficiency.», Estimates Frédéric Altare, immunologist and Inserm research director in Nantes. In terms of accessibility, Moderna’s vaccine is much easier to obtain today, which reduces waiting times: France currently has 5 million doses of Pfizer, for 20 million doses of Moderna.

For people who have received the AstraZeneca vaccine (whether one or two doses), the booster remains an RNA vaccine. The combination of two different technologies would even be interesting from an immune standpoint, according to P^r Hare. The “heterologous prime-boost”, or “vaccine mix”, is “a mechanism known in immunology and very widely used in the past. It is already used with the pneumococcal vaccine in adults, or the Ebola vaccine from Janssen. The order of the vaccines is also important: the Pfizer-Pfizer-AstraZeneca sequence is not as interesting as AstraZeneca-AstraZeneca-Pfizer.»

“Omicron seems to leave less hold to the antibodies”

As for the probable arrival of the new Omicron variant in France, it also pleads in favor of a third dose, even if the results are for the moment very limited on the subject. The first studies show for the moment that a vaccination with two doses of Pfizer would not generate enough antibodies to neutralize the virus. “Due to its mutations, Omicron seems to leave less hold on antibodies induced by vaccination. We therefore imagine that it will take more to neutralize it. However, with the booster, the number of circulating antibodies is boosted by a factor of 35 compared to the first two doses.», Explains Frédéric Altare.

Read alsoOmicron variant: what worries, what reassures

The British health authorities, who have already identified several hundred cases of the Omicron variant and began their recall campaign long before us, were able to make a preliminary estimate of the effectiveness of the recall: it would protect from 70 to 75% of symptomatic forms. mild disease caused by Omicron (compared to 90% for the Delta variant). The sample is still too small to have a good idea of ​​the protection conferred against the severe forms, on the other hand the reduction in the number of infections remains nevertheless a major issue because, “the more we let people get infected, the more we take the risk of seeing new mutations appear», Recalls Frédéric Altare.

SEE AS ​​WELL – Omicron appears to have ‘increased risk of reinfection’ but less severe symptoms, WHO says

For Jean Castex, vaccinating children over 5 years old has become “a necessity”

Prime Minister Jean Castex estimated Sunday in an interview with France Bleu Alsace that the vaccination of children aged 5 to 11 against Covid-19 was “a necessity”. The youngest “Are transmitters” of the virus, he justified. “I am a living example. It was my 11 year old daughter who gave me the virus a few weeks ago. ”

Read alsoVaccinating children against Covid, good or bad idea?

In a notice published on December 6, the Orientation Council for the vaccination strategy considered that “The indications for the vaccination of children aged 5 to 11 appear to have been met”. It nevertheless conditioned its implementation on obtaining data. “In real life” to assure “That the risk-benefit balance is favorable”, which could occur after obtaining the American data, “Possibly from the end of December”. According to a document from the Ministry of Health consulted by AFP shortly before the last Health Defense Council, “The opening of vaccination to all children” of this age group would be expected “Beginning of January 2022”.

At the end of this Defense Council, Jean Castex declared that the government was considering opening the vaccination against Covid-19 “To all children” from 5 to 11 years old, “On a voluntary basis, if possible by the end of the year”. Since the beginning of December, Switzerland, Spain and Portugal have authorized the vaccination of 5-11 year olds.

Tristan Vey with AFP

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