Rise of coronavirus variants will define the next phase of the pandemic in the U.S.

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. In addition to those three variants, the CDC considers two in California "variants of concern" and is watching them closely. Described by Indian researchers on March 24, it was first identified in the United States March 25 in a patient in the San Francisco Bay area. But physicians and health officials in Brazil say it has signaled a darker and deadlier phase of the pandemic. The vaccination rate in Brazil is lagging far behind the rate in the United States.