Are Covid vaccine boosters effective? According to a French study published on Tuesday, they do strengthen protection against severe forms of the disease, including against recent incarnations of the virus, but this effect is rapidly diminishing. "The booster doses made it possible to strengthen the protection against the risk of hospitalization, but this protection remained limited in time," concludes this work written under the aegis of the National Agency for the Safety of Medicines (ANSM) and the 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 Covid vaccines since their introduction in early 2021.

Study data on successive recalls

The anti-Covid vaccination has demonstrated its effectiveness against severe forms, even if it does little to 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 health authorities to organize booster campaigns, called third, fourth and fifth dose. However, there was a lack of data on the real benefits of these successive recalls, especially after the appearance of the Omicron variant. The latter, which has gone through several incarnations, escapes the immune response more easily.

The study – conducted under the direction of epidemiologist Mahmoud Zureik – looked at the case of patients hospitalized for Covid between June and October 2022. The researchers compared their vaccination situation with that of a group of people who had not been hospitalized, a so-called case-control procedure.

Effective reminders, but in the short term

First, it appears that vaccines have remained highly effective against the risk of hospitalization, even against Omicron. This is the case in people who have received only their first two doses, but this protection is further increased by boosters: the effectiveness 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 recalls quickly diminishes over time. After six months, there is little difference compared to people who have only had one vaccination. These results therefore imply that vaccination campaigns must be well targeted in relation to Covid waves, a difficulty increased by the fact that they are much more frequent and irregular than, for example, seasonal influenza.

  • Health
  • Covid 19
  • Anti-covid vaccine
  • Vaccination
  • study