Booster efficacy wanes after 4 months, still offers high protection against hospitalization, CDC finds

The effectiveness of mRNA COVID-19 boosters drops after about four months, though they still offer significant protection against hospitalization, according to a CDC study conducted during the omicron surge. 

The CDC's Feb. 11 Morbidity & Mortality Weekly Report found vaccine efficacy against emergency department and urgent care visits for COVID-19 was 87 percent during the first two months after receiving a booster, dropping to 66 percent by the fourth month. Meanwhile, protection against hospitalization was 91 percent in the two months after the third dose, falling to 78 percent after four months. 

"For both delta- and omicron-predominant periods, [vaccine efficacy] was generally higher for protection against hospitalizations than against [ED/urgent care] visits," researchers said.  "All eligible persons should remain up to date with recommended COVID-19 vaccinations to best protect against COVID-19-associated hospitalizations and ED/UC visits."

The findings are based on a multistate analysis of 241,204 ED/urgent care visits and 93,408 hospitalizations among adults with COVID-19-like illness between Aug. 26, 2021, and Jan. 22, 2022. 

To view the full report, click here.

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