Vaccine effectiveness against COVID-19 infection dropped from 91% to 66% once the delta variant accounted for the majority of circulating virus, according to a study published Tuesday by the U.S.

Moderna on Tuesday released preliminary data indicating its vaccine is likely to hold up against several variants of concern, including the Delta variant, which is predicted to become the dominant ...

The delta variant is fueling the COVID-19 surge in the United States, but experts warn that a more dangerous variant could emerge if more Americans don't get vaccinated. Delta is the most recent of ...

SAN FRANCISCO -- Earlier in the pandemic, experts had hoped if we can get 75% of Americans vaccinated, we can contain the coronavirus. Thursday, we're at just over 50% vaccinated. But 75% is no longer ...

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center. More recent studies — but not all — show waning effectiveness of the mRNA vaccines to prevent ...

A third dose of the Pfizer/BioNTech COVID-19 vaccine can "strongly" boost protection against the delta variant -- beyond the protection afforded by the standard two doses, suggests new data released ...

We all watched the news: a new variant of the SARS-CoV-2 virus was found in India in October 2020, sparking a devastating second wave with more than 400,000 daily infections. This mutation called ...

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center. At a recent town hall meeting in Cincinnati, Ohio, President Joe Biden was asked about COVID-19 ...

NEW YORK, N.Y. — Pfizer announced Wednesday that data shows a third dose of its COVID-19 vaccine can “strongly” boost protection against the highly transmissible delta variant. The pharmaceutical and ...