A fishing vessel that left Seattle in May returned with an unexpected catch: the first direct evidence in humans that antibodies to the coronavirus can thwart infection.

More than a hundred crew members aboard the American Dynasty were stricken by the infection over 18 days at sea. But three sailors who initially carried antibodies remained virus-free, according to a new report.

HENDERSONVILLE, N.C. — The coronavirus entered Cherry Springs Village quietly, then struck with force. Nearly every staff member and resident of the long-term care facility would become infected.

They needed help — fast — and the county responded: It sent in a “strike team” of medical workers, emergency responders, clergy and others, in what is becoming a new model for combating Covid-19 in residential care centers.

Nurses and doctors from hours away came to aid sick residents and replace staff who had contracted the virus. They set up oxygen and IV drips, to avoid sending residents with milder illness to overburdened hospitals.

Last week, just as the Food and Drug Administration was preparing to issue an emergency authorization for blood plasma as a Covid-19 treatment, a group of top federal health officials including Dr. Anthony S. Fauci intervened, arguing that emerging data on the treatment was too weak, according to two senior administration officials.

The authorization is on hold for now as more data is reviewed, according to H. Clifford Lane, the clinical director at the National Institute of Allergy and Infectious Diseases. An emergency approval could still be issued in the near future, he said.