Are Covid vaccine boosters effective? According to a French study published on Tuesday, they do enhance protection once morest severe forms of the disease, including once morest recent incarnations of the virus, but this effect is rapidly diminishing. “The booster doses made it possible to reinforce protection once morest the risk of hospitalization, but this protection remained limited in time”, concludes this work written under the aegis of the National Medicines Safety Agency (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.
Study data on successive recalls
Anti-Covid vaccination has demonstrated its effectiveness once morest serious forms, even if it does not reduce the risk of being contaminated in the medium or long term. However, even once morest 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 following the appearance of the Omicron variant. The latter, which has known several incarnations, escapes the immune response more easily.
The study – 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 not who have not been hospitalized, a so-called control case procedure.
Effective but short-term reminders
First of all, it shows that the vaccines have kept a good efficiency once morest 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 once morest hospitalizations is estimated at 45% following a primary vaccination, 56% for a third dose and 75% following 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.
