Covid19. Why does HAS not (yet) recommend generalizing the fourth vaccine dose?

The government has made it possible for people in their 80s and severely immunocompromised to receive a second booster dose three months or more after the previous booster.

Weakened vaccine efficacy with Omicron

At the end of last week, the Supreme Health Authority has already recommended this fourth injection for those over the age of 65 and especially those most at risk.

Immune escape of the virus is confirmed every month, especially against the Omicron variant and even with the BA.2 sub-variant. Also, the efficacy of the vaccine decreases over time as the subject is aged and/or frail.

In principle, a booster dose, also called a “booster”, is expected to increase the protection of the vaccine tenfold. By administration of the third dose, the antibody levels observed appeared ten to 50 times higher than those recorded after the first two injections.

Fourth dose to restore protection

The fourth dose did not show such efficacy: most often it shows “small benefits” by restoring the level of antibodies provided by the previous booster. In other words, it does not “increase” protection. But it restores it: according to the latest data, it halves the risk of infection and greatly reduces the risk of a serious form or death.

It is this argument that justifies this new reminder for those who are more exposed to the virus because of the most fragile, tired or dysfunctional immune system. For those over 80 and the immunocompromised, the reason is certain: this second reminder has been available since 14 March.

A second “useful” reminder

For 65-79 year olds, not yet. But the observation is clear: the Supreme Health Authority considers this fourth dose to be beneficial “for people over 65 who are desiring and at very high risk for a severe form of the disease or who are polypathological.”

latest data […] show that people aged 65 and over are still most at risk […]. As of March 10, over 60 years of age represented 80% of patients hospitalized with Covid-19.


HAS also reminds that “in people aged 60 and over, the protection provided by the booster dose begins to decrease after 3 months”.

The “vaccine compliance” of the population in question

Thus, for the most vulnerable, reinvigorating immunity by stimulating a new booster dose appears beneficial for HAS – even if it means simply “rebuilding” that previous level of immunity.

And for the rest of the population? Not yet, in essence it responds to HAS. He reports that for the time being, there is a risk of a decrease in “population adherence to vaccines with very frequent reminders.”

In the case of a second reminder, the HAS therefore recommends respecting “preferably an interval of at least 6 months with the first reminder”. This could herald a new vaccine boost in the general population this summer, or more likely at the beginning of the school year.

Many uncertainties

And again: everything will depend on the epidemic situation: will the virus still continue to circulate so strongly? Will a new variant appear? Will other vaccines be available that are more effective against the variants? Will the epidemic be behind us? There are many questions that create “uncertainty” in the context of the epidemic that HAS notes.

It is also a reminder that vaccine efficacy remains “good (over 70% in hospitalizations) three months after initial booster administration)” among those under 60 years of age.

The HAS considers it inappropriate to recommend the administration of a second booster dose in the general population at this time.


Towards new vaccines?

The health authority recommends first “develop a medium and long-term vaccination strategy before rolling out the recall to the general population” – what it envisions for next fall:

Consideration is underway to make recommendations for a medium- and long-term anti-Covid-19 vaccine strategy, especially considering the imminent arrival of new vaccines and vaccines adapted to different variants in circulation, all available immunological and clinical data as well as population acceptability issues.


According to the managing director of the Franco-Austrian company, the French vaccine, specifically from Valneva, should arrive in France in May. It was announced with a high efficiency compared to the Omicron. As for messenger RNA vaccines, new formulas are being developed.

Continuing the primary vaccination effort

Finally, HAS recalls that currently “only 74.3% of people over 80 receive booster vaccines”.

It also highlights the “importance of continued efforts to vaccinate the oldest people who have not yet been vaccinated or have received additional doses, particularly those for whom full vaccine coverage is still insufficient.”

Finally, the HAS reminds that “it is essential for optimal protection that the entire target population benefit from a vaccination program with the highest efficacy that supports the use of mRNA vaccines in the absence of contraindications.”