How long are we protected after injecting a third dose of messenger RNA Covid-19 vaccine? The Centers for Disease Control and Prevention (CDC) conducted a large study across the United States between August 2021 and January 2022 to answer this question. Here are the results.
Decline in immunity 4 months after injection
About fifteen American medical centers monitored emergency room visits and hospitalizations linked to Covid-19 infection in order to monitor the effectiveness of the third vaccine dose. In total, these are nearly 100,000 hospitalizations that have been analyzed. As already observed for the primary vaccination, the data show that immunity wanes a few months after the booster.
Specifically, the CDC study estimates that the third dose of an mRNA vaccine against Covid-19 protects up to 87% for ER admission and 91% for ICU admissions. But four months after this booster dose, the effectiveness drops to 66% for admission to the emergency room and 78% for intensive care.
However, these data should be put into perspective, because this study does not mention the effects of this third dose on mild and asymptomatic forms Sars-CoV-2 infection. It also does not take into account health problems or the condition of patients before their infection.
Anti-Covid-19 vaccine: towards a fourth dose?
The study shows that the effectiveness of the vaccine with regard to consultations related to Covid-19 was higher after the third dose than after the second dose. “mRNA vaccines, including the booster dose, are very effective, but the effectiveness decreases over time. Our results suggest that an additional dose may be necessary to maintain protection against Covid-19, mainly in high-risk populations,” explains Brian Dixon, scientist at the Regenstrief Institute and lead author of the study.
In France, this question of the fourth dose of vaccine against Covid-19 is already posed for the government. The Minister of Health Olivier Véran deemed it “possible” the use of a new booster injection in the fall, on the set of our colleagues from BFMTV on February 2. For immunocompromised people, this injection could even become a annual dose like that of the seasonal flu. In mid-January, the Vaccine Strategy Orientation Council (COSV) published a unfavorable opinion on the generalization of a fourth dose of vaccine.
“With the exception of severely immunocompromised people, a second vaccine booster dose would not bring any significant individual benefit”, specified the COSV.
Other countries have decided to launch a new vaccination campaign to administer a 4th dose to the population. This is the case of Israel, Belgium, Denmark and even Chile.
