COVID-19 mRNA vaccines less effective for Delta variant, study shows

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In a new study from the CDC COVID-19 Response Team, researchers found 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.

In the study, the team analyzed weekly data reported by Centers for Medicare & Medicaid-certified skilled nursing facilities or nursing homes.

They examined 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 effectiveness against infection for any mRNA vaccine was 74.7&in the pre-delta period using 17,407 weekly reports from 3,862 facilities.

During an intermediate period (May 10 to June 20), the effectiveness was 67.5% using 33,160 weekly reports from 11,581 facilities.

During the delta period, the effectiveness was 53.1% using 85,593 weekly reports from 14,917 facilities. Similar effectiveness estimates were reported for the Pfizer-BioNTech and Moderna vaccines.

The team says 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.

An additional dose of the COVID-19 vaccine might be considered for nursing home and long-term care facility residents to optimize a protective immune response.

If you care about COVID, please read studies about a single dose of the Moderna or Pfizer COVID-19 vaccine may not be enough to reliably ward off infection and findings of the cause of blood clots in people with severe COVID-19.

For more information about COVID and your health, please see recent studies about antibodies from COVID-19 vaccination almost 3 times higher than from infection and results showing that aspirin and other common anti-inflammatory drugs could help prevent COVID-19 deaths.

The study is published in the U.S. Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report. One author of the study is Srinivas Nanduri, M.D.

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