The third dose of the anti-Covid vaccine has been available to everyone since the end of November 2021. Here we are a few months later, what do we know about the duration of the protection it confers? In the US, the CDC did the math.
The CDC (Centers for Disease Control and Prevention) conducted an extensive study across the United States to answer an as yet unanswered question, how long does theimmunity conferred by the third dose messenger RNA anti-Covid-19 vaccines ? Between August 2021 and January 2022, fourteen American medical centers located in ten different states monitored emergency room visits and hospitalizations for Covid-19 in order to estimate the effectiveness of the third vaccine dose. Unsurprisingly, the study reports a trend similar to what was observed with the primary vaccination. Vaccine immunity declines in a few months, at the same time reducing the effectiveness of vaccines against symptomatic and severe forms of Covid-19.
The third dose weakens four months after the injection
If we take the wave Delta as reference, the arrival of Omicron reduced the overall effectiveness of vaccines by one notch. The booster dose is no exception to the rule. The CDC study estimated that a third dose of a vaccine mRNA for Covid-19 prevents 87% and 91% of emergency department visits and hospitalizations, respectively. Data obtained two months after the injection. Four months after the injection, the efficacy of the third dose drops to 66% and to 78% against emergency room visits and severe forms.
An important element is still missing: the effectiveness of the third dose on infections. CDC-led tracking focuses on hospitalizations, so asymptomatic or mild infections that didn’t get people to the hospital aren’t counted here. ” mRNA vaccines, including the booster dose, are very effective, but the effectiveness decreases over time. Our results suggest that an additional dose may be needed to maintain protection against Covid-19, primarily in high-risk populations », says Brian Dixon, scientist at the Regenstrief Institute and lead author of the study.
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