COVID vaccines’ effectiveness against infections ebbs over time, but they still protect against death, study finds

As the delta variant became the dominant strain of coronavirus across the United States, all three COVID-19 vaccines available to Americans lost some of their protective power, according to a new study.

Researchers who scoured the records of nearly 800,000 U.S. veterans found that in early March, just as the delta variant was gaining a toehold across American communities, the three vaccines were roughly equal in their ability to prevent infections.

But over the next six months, that changed dramatically.

By the end of September, Moderna’s two-dose COVID-19 vaccine, measured as 89% effective in March, was only 58% effective.

The effectiveness of the Pfizer vaccine, which also employs two doses, fell from 87% to 45% in the same period.

And most strikingly, the protective power of Johnson & Johnson’s single-dose vaccine plunged from 86% to just 13% over those six months.

Nevertheless, the vaccines remained protective against death in people infected during the delta surge and the risk of death was highest among unvaccinated people, the study found. (Read more)