The Food and Drug Administration said on Monday that vaccine developers would not need to conduct lengthy randomized controlled trials for vaccines that have been adapted to protect against concerning coronavirus variants. The recommendations, which call for small trials more like those required for annual flu vaccines, would greatly accelerate the review process at a time when scientists are increasingly anxious about how the variants might slow or reverse progress made against the virus.

The guidance was part of a slate of new documents the agency released on Monday, including others addressing how antibody treatments and diagnostic tests might need to be retooled to respond to the virus variants.

Together, they amounted to the federal government’s most detailed acknowledgment of the threat the variants pose to existing vaccines, treatments and tests for the coronavirus, and came weeks after the F.D.A.’s acting commissioner, Dr. Janet Woodcock, said the agency was developing a plan.