The quickest way to assess immunity is a blood test that looks for protective antibodies in the blood of people who have recovered. But first you have to have the test.
Antibody tests are used in Singapore, China and a handful of other countries. But they are just coming to market in much of the West.
Last week, Dr. Krammer and his colleagues
developed one such antibody test that could be scaled up in “days to weeks,” he said.
The team validated the test in blood plasma taken from three patients with Covid-19. The researchers are seeking speedy approval from the F.D.A.