How does the Delta variant dodge the immune system? Scientists find clues.
One dose of vaccine is not enough to protect against the Delta and Beta variants, new research suggests, and even people who have had Covid-19 should be immunized.
More Contagious Virus Variant Is Now Dominant in U.S., C.D.C. Chief Says
The B.1.1.7 variant, first identified in Britain, is now the source of most new coronavirus infections in the United States, the director of the Centers for Disease Control and Prevention said.