In his report published Tuesday, Epi-Phare shows that people who had a third dose before being infected with omicron benefit from the best immunity against Sars-Cov-2.
by Delphine Roucaute
Third, fourth, fifth dose: many French people have not known to sort between the various recommendations communicated by the health authorities since the introduction of the first reminders, in September 2021. “The question that arises today ‘ Hui, it is rather to know what is the effectiveness of the last dose that we received, whether it is the third, the fourth or the fifth, and for how long we are protected, “sums up Mahmoud Zureik, the Director of Epi-Phare, a scientific interest group placed under the double supervision of the National Agency for the Safety of Medicines and the National Health Insurance Fund.
It is to this question that his team provides several answers in a report, published Tuesday, February 21, relating to the effectiveness of vaccination recall doses on the risk of hospitalization for COVID-19.
The authors of the report have crossed data from various information systems in order to take into account the vaccination status and the chronology of positive tests of hospitalized patients between June and October 2022. It is in their extreme majority People affected by one of the omicron subvariants, at a time when a second dose of recall had been recommended for people aged 60 and over, and before the introduction of bivalent vaccines targeting Ba. 4 and BA.5 . Work of a particular methodological complexity, since “many people have had COVVID, possibly several times, and have been vaccinated according to different diagrams and chronologies. Some were positive before being vaccinated, sometimes between two doses, Sometimes after vaccination “, lists Mahmoud Zureik.
First element, which seems today acquired but which was far from obvious at the start of the vaccination campaign: even after two years, people having received only two doses of vaccine, it is -Ades a simple primary vaccination, are always better protected than non-vaccinated in the face of the serious forms of COVID-19, with an effectiveness of 45 % against the risk of hospitalization. This protection then increases at each dose of recall, gradually decreasing in the months following each injection.
robustness of hybrid immunity
Regarding the interest of recall doses compared to a first-time vaccinacy, the authors believe that “the additional effectiveness of a recall dose (third, fourth or fifth dose) was estimated at 69 % in both first months following the injection “. It then only decreases in the following months, 55 % between two and four months, to 30 % between four and six months and finally to 22 % beyond six months.
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