What should I know about the delta variant?

It's the most contagious coronavirus mutant so far in the pandemic, but COVID-19 vaccines still provide strong protection against it. Nearly all hospitalizations and deaths are among the unvaccinated.

Still, the U.S. Centers for Disease Control and Prevention cited the delta's surge for its updated advice that fully vaccinated people return to wearing masks indoors in areas with high transmission. The change is based on recent research suggesting that vaccinated people who get infected with the delta variant can spread it to others, even if the vacci...