A study published on Tuesday, February 21, now confirms it: reminders of the anti-Covid vaccine reinforce protection against serious forms of the virus. But this effect diminishes rapidly. These conclusions are drawn of a French study carried out by the National Agency for the Safety of Medicines (ANSM) and the Health Insurance as part of the “EPI-PHARE” vaccine monitoring system. Its objective was to evaluate the effectiveness of booster doses for RNA-messenger vaccines only (Pfizzer and Moderna), against the risk of infection due to Omicron sub-variants. This is the latest episode in a series of works that have been monitoring the effectiveness of anti-Covid vaccines since their birth in 2021.
Vaccination has long demonstrated its effectiveness against severe forms. But 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. Few data were available on the effectiveness of the latter, in particular since the appearance of Omicron, which escapes the immune response more easily thanks to its many developments.
Protective but not lasting reminders
The EPI-PHARE study compared the vaccination situation of a group of 39,000 patients hospitalized between June and October 2022, with that of a control group who had never been hospitalized. It shows that the vaccines have well protected their hosts against the risk of hospitalization. Efficacy against hospitalizations is estimated at 45% after a primary vaccination, 56% for a third dose and 75% after a fourth or fifth dose: it therefore increases with boosters. “The level of efficacy is all the more important as the number of doses received is high or the time since the last dose is short”, also specifies the study.
The researchers nevertheless observed a decrease in the effect of these reminders over time. Six months after receiving a booster, the subjects observed showed almost no difference with those who received only a primary 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.
The effectiveness of hybrid protection confirmed
This study also verified another important point: the veracity of hybrid immunity, that is to say the immunity acquired by people with one or more infections, and vaccination. Combined with a booster, an infection even turns out to be the best protection against future serious forms. “The efficiency of hybrid immunity was estimated at 82% compared to people who did not receive a second booster dose and who did not have a post-third dose infection”, indicates the study.
This information makes it possible to know that for a person who has already received three doses of vaccine, a fourth booster dose is therefore not necessary quickly after an infection to protect against serious forms. Similar results have also been published by The Lancet a few days ago. With this new knowledge, the objective for the health authorities will now be to define the right rhythm of vaccination reminders in anticipation of waves of contamination, to optimize the protection of the population.