The internal CDC document said the Delta variant was more transmissible than the viruses that cause MERS, SARS, Ebola, and the seasonal flu.

The more contagious Delta variant of Covid-19 now makes up 83% of sequenced samples in the United States, US Centers for Disease Control and Prevention Director Dr. Rochelle Walensky said Tuesday.

"The rules have changed. We have a different epidemic now that we did in May." Adding more insight into the CDC’s updated mask guidance, newly published details of the Provincetown outbreak raise ...