The Food and Drug Administration’s chief tobacco regulator has been forced out.

The warning letters are not legally binding, but the government can take companies to court if they are ignored. Antibody tests are different from the nasal swab tests used to diagnose most active infections. Antibody tests were initially thought to have a key role in identifying people who have developed some immunity to the virus. And even well-performing antibody tests can sometimes produce more false results than accurate ones. Meanwhile, roughly 190 antibody tests launched under the agencys previous policy are awaiting review.