mRNA COVID-19 Vaccine Effectiveness Lower During Delta Strain Era

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by Healthday

Adjusted effectiveness 53.1 percent against infection in nursing home residents during period when delta strain was predominant

FRIDAY, Aug. 20, 2021 (HealthDay News) — mRNA COVID-19 vaccines provide protection against infection among nursing home residents, but the vaccine effectiveness was lower after the delta variant became the predominant strain, according to research published in the Aug. 18 early-release issue of the U.S. Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report.

Srinivas Nanduri, M.D., from the CDC COVID-19 Response Team, and colleagues analyzed weekly data reported by Centers for Medicare & Medicaid-certified skilled nursing facilities or nursing homes to assess effectiveness of full vaccination with the two currently authorized mRNA COVID-19 vaccines soon after vaccine introduction (March 1 to May 9, 2021; pre-delta period) and when the delta variant predominated (June 21 to Aug. 1, 2021).

The researchers found that the adjusted effectiveness against infection for any mRNA vaccine was 74.7 percent in the pre-delta period using 17,407 weekly reports from 3,862 facilities. During an intermediate period (May 10 to June 20), the adjusted effectiveness was 67.5 percent using 33,160 weekly reports from 11,581 facilities. During the delta period, the adjusted effectiveness was 53.1 percent using 85,593 weekly reports from 14,917 facilities. Similar effectiveness estimates were reported for the Pfizer-BioNTech and Moderna vaccines.

“To prevent transmission of SARS-CoV-2 in nursing homes, these findings highlight the critical importance of COVID-19 vaccination of staff members, residents, and visitors and adherence to rigorous COVID-19 prevention strategies,” the authors write. “An additional dose of COVID-19 vaccine might be considered for nursing home and long-term care facility residents to optimize a protective immune response.”

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