.
WASHINGTON — Variants of the coronavirus are increasingly defining the next phase of the pandemic in the United States, taking hold in ever-greater numbers and eliciting pleas for a change in strategy against the outbreak, according to government officials and experts tracking developments.
The highly transmissible B.1.1.7 variant that originated in the United Kingdom now accounts for 27% of all cases in this country. It is the most common variant in the United States, Rochelle Walensky, director of the Centers for Disease Control and Prevention, said Wednesday — a development that officials predicted months ago. Two other variants, which took root in South Africa and Brazil and also are more transmissible, are cropping up with increasing frequency in parts of the United States.