A New Hampshire National Guard member vaccinates a man at a drive-through center in Londonderry, N.H. (Joseph Prezioso/AFP/Getty Images)

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.