Virus Variants Spur Warnings Amid Hopeful Vaccine Data (1)

The Biden administration has increased monitoring for new variants of the coronavirus that spread more easily, including one that could become the dominant strain in the U.S. by March.

The U.S. is asking each state to send at least 750 samples a week to be sequenced to determine what mutations are spreading, Centers for Disease Control and Prevention Director Rochelle Walensky said in a briefing with reporters Friday.

Yet she warned that the existing system to detect different strains is too slow for public health interventions to contain them.

“By the time someone has symptoms, gets a test, has a ...