COVID-19 boosters wane over time but remain protective, study finds
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The effectiveness of a COVID-19 booster shot waned over time, but the extra dose continued to protect against hospitalization at 4 months and beyond, according to data collected during the omicron surge and reported Friday in MMWR.
The study showed that a booster dose of messenger RNA vaccine was more than 90% effective at preventing hospitalization during the first 2 months, dropping below 80% by 4 months, according to CDC epidemiologist Jill M. Ferdinands, PhD, and colleagues.
The study assessed 241,204 ED and urgent care encounters and 93,408 hospitalizations occurring among adults with COVID-19 in 10 states from Aug. 26, 2021, through Jan. 22, 2022. They found that vaccine efficacy after three shots was lower during the omicron surge than at any point when delta was the predominant variant.
During omicron, protection against ED or urgent care visits was 87% during the first 2 months after a third mRNA dose and decreased to 66% after 4 to 5 months. Effectiveness against hospitalization was 91% during the first 2 months and decreased to 78% by 4 months after the third dose.
“For both delta- and omicron-predominant periods, vaccine efficacy was generally higher for protection against hospitalizations than against ED/urgent care visits,” the authors wrote.
Among the total ED or urgent care visits, 77% occurred during the delta period and the rest during the omicron surge. Among all visits, 46% of patients were unvaccinated, 44% received a primary series and 10% had received three doses.
An even higher proportion of hospitalizations — 89% — occurred during the delta-predominant period. Among those who were hospitalized, 43% were unvaccinated, 45% had received a two-dose primary series and 12% had received a third booster dose.
“These findings underscore the importance of receiving a third dose of mRNA COVID-19 vaccine to prevent both COVID-19-associated ED/urgent care encounters and COVID-19 hospitalizations among adults,” the authors wrote. “The finding that protection conferred by mRNA vaccines waned in the months after receipt of a third vaccine dose reinforces the importance of further consideration of additional doses to sustain or improve protection against COVID-19-associated ED/urgent care encounters and COVID-19 hospitalizations.”
A second study by CDC epidemiologist Anne M. Hause, PhD, and colleagues assessed booster-related reports submitted to two CDC vaccine safety monitoring systems — v-safe, a voluntary smartphone-based system, and the Vaccine Adverse Event Reporting System (VAERS) — from Sept. 22, 2021, through Feb. 6, 2022.
Among 39,286 people who reported adverse events to VAERS, 92.4% said their reactions were not serious. The most commonly reported symptoms were headache (13.3%), fever (13.2%) and muscle pain (12.6%).
People who received the same mRNA vaccine for all three shots experienced fewer adverse reactions following the booster dose than they did after their second dose, the researchers found.
References:
Ferdinands JM, et al. MMWR Morb Mortal Wkly Rep. 2022;doi:10.15585/mmwr.mm7107e2.
Hause AM, et al. MMWR Morb Mortal Wkly Rep. 2022;doi:10.15585/mmwr.mm7107e1.
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