According to a French study, booster doses of anti-Covid vaccines are effective in combating severe forms, but their effect decreases rapidly.
A French study, published on Tuesday, confirms the effectiveness of vaccine boosters against severe forms of Covid-19, including its latest variants and sub-variants. However, it shows that this efficacy decreases rapidly after injection of the booster dose.
The booster doses made it possible to strengthen protection against the risk of hospitalization, but this protection remained limited in time”, concludes the report of the National Agency for the Safety of Medicines (ANSM) and Health Insurance.
This study, not yet published in a scientific journal, is the latest episode in a series of studies that have looked at the effectiveness of anti-Covid vaccines since their introduction in early 2021.
The study fills a data gap
Anti-Covid vaccination, which in France is essentially based on vaccines from Moderna and Pfizer/BioNTech, has demonstrated its effectiveness against serious forms, even if it does not reduce the risk of being contaminated in the medium or long term.
However, even against hospitalizations, the effectiveness tends to decrease over time, which has led the health authorities to organize recall campaigns, known as third, fourth and then fifth doses.
However, there was a lack of data on the real benefits of these successive boosters, in particular after the appearance of the Omicron variant. The latter, which has known several incarnations, escapes the immune response more easily.
The study published on Tuesday – carried out under the direction of epidemiologist Mahmoud Zureik – looked at the case of patients hospitalized with Covid between June and October 2022. The researchers compared their vaccination situation with that of a group of people who have not been hospitalized, a so-called control case procedure.
Targeting vaccination campaigns
First of all, it shows that the vaccines have kept a good efficiency against the risk of hospitalization, even in the face of Omicron. This is the case in people who have only received their first two doses, but this protection is further increased by boosters: efficacy against hospitalizations is estimated at 45% after a primary vaccination, 56% for a third dose and 75% after a fourth or fifth dose.
But the effect of these reminders quickly diminishes over time. After six months, there is little difference compared to people who have only had one vaccination.
These results therefore imply properly targeting vaccination campaigns in relation to the waves of Covid, a difficulty increased by the fact that they are much more frequent and irregular than, for example, the seasonal flu.
