A new study of more than 780,000 United States Veterans shows that, although vaccination remains protective against SARS-CoV-2 infection, protection waned as the Delta variant emerged in America.
“Our findings support the conclusion that COVID-19 vaccines remain the most important tool to prevent infection and death. Vaccines should be accompanied by additional measures for both vaccinated and unvaccinated persons, including masking, hand washing, and physical distancing.”
The mRNA vaccines by Pfizer-BioNTech and Moderna and the viral vector vaccine by Janssen have effectively prevented clinically significant disease caused by SARS-CoV-2 since their rollout in the United States in late 2020. However, by July 2021, the United States experienced a surge in cases of COVID-19, dominated by the Delta variant. Breakthrough infections and deaths have since continued to emerge in vaccine recipients.
National data on vaccine breakthroughs are limited in the United States. To address this gap, Barbara Cohn et al. examined SARS-CoV-2 infection and deaths by vaccination status in more than 780,000 Veterans during the period February 2021 to October 2021, a time encompassing the emergence of the Delta variant.
Vaccine type differed by age; younger Veterans were more likely to have received Janssen’s vaccine. By October 2021, the protection against infection offered by mRNA vaccines declined from about 87% to 41%. For the viral vector vaccine, the protection against infection declined to about 13%. Protection against death remained high for all vaccine types (and especially so for Pfizer-BioNTech and Moderna), and compared to unvaccinated Veterans, those fully vaccinated had a much lower risk of death after infection. Unvaccinated individuals remained at the highest risk of infection, severe disease and death. Findings support continued efforts to increase vaccination and booster campaigns, and to advocate for multiple additional layers of protection against infection.
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