The effectiveness of the third dose of vaccine decreases over time, but it continues to offer significant protection against the risk of severe disease.
- In France, the third dose concerns people over the age of 18, from three months after the last injection.
- The study focused on people positive for Covid-19, having gone to emergency services.
- It started 14 days after the first American recommendations concerning the third dose of vaccine.
The effectiveness of vaccines against Covid-19 decreases over time. For this reason, it is recommended to receive a third dose of the serum to improve the level of protection. But what happens in the months following this injection? This is the question asked by researchers at the Regenstrief Institute in the United States. With the Centers for Disease Prevention and Control (CDC), they worked on the effectiveness of the third dose of messenger RNA vaccine, in a study published on February 11.
Declining efficiency over time, regardless of variant
The authors were based on data collected between August 2021 and January 2022. The analysis of these shows that people who received the second and third doses of an mRNA vaccine were better protected against the risk of hospitalization. The authors note, however, that the effectiveness of the vaccine was also lower overall during the Omicron wave than during the Delta wave. Regarding the risk of visiting the emergency room during this period, it fell from 97% during the first two months following the booster dose to 89% four months later. During the Omicron wave, which started at the beginning of winter 2021, this efficiency was 87% during the first two months after the third dose, then it increased to 66% four months after this injection. Protection against the risk of hospitalization also decreases over time. After the third dose, and in the case of the Delta variant, it goes from 96% two months after the injection to 76% after four months or more. For the Omicron variant, it is 91% during the first two months, and decreases to 78% at four months.
Reduced but continuous protection
“mRNA vaccines, including booster, are very effective, but their effectiveness decreases over time”, summarizes the co-author of the study, Brian Dixon. With his co-authors, he notes that protection against the risk of severe form remains important in the months that follow, despite this decline. “Our results suggest that additional doses may be needed to maintain protection against Covid-19, especially for high-risk populations.“Some countries did not wait for this study to recommend another booster dose for those most at risk. Last December, the Israeli government authorized a fourth dose for people over 60, those with fragile health. and for caregivers.This campaign was interrupted at the beginning of January, pending clinical studies on the effectiveness of this reminder.
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