The Food and Drug Administration said it will propose guidelines on how manufacturers of coronavirus vaccines, therapeutics and diagnostic tests should deal with new variants of the virus. Janet Woodcock, the administration’s acting commissioner, noted that the FDA has anticipated the emergence of variants and does not believe there will be “the need to start at square one with any of these products.”

Earlier, the pharmaceutical company Johnson & Johnson applied for emergency-use authorization after its single-shot vaccine proved to be “robustly effective” against illness in a global trial — and especially at preventing severe disease and death.

Here are some significant developments:

  • About 35.2 million doses of the coronavirus vaccine have been administered in the United States, according to data published Thursday by the Centers for Disease Control and Prevention.
  • Wisconsin Gov. Tony Evers (D) issued a new emergency mask mandate Thursday, minutes after the Republican-controlled legislature repealed his previous order, which had been in place since August.
  • At least eight Democratic senators, including newly elected John Hickenlooper (Colo.), voted in a favor of a GOP amendment to block stimulus payments to undocumented immigrants.
  • Britain has launched a 13-month study to determine whether mixing vaccine doses — in this case, Pfizer-BioNTech and AstraZeneca — still protects people from infection.
  • Health experts, including Anthony S. Fauci, are warning Americans to avoid large Super Bowl parties. “The Super Bowl doesn’t have to be a superspreader event,” former Centers for Disease Control and Prevention director Tom Frieden said on Twitter.