Just 150 or so of the 30,000 or more subjects enrolled in each trial need to be infected and show symptoms to provide the data to assess the vaccines, according to a Wall Street Journal review of researchers’ plans for U.S. studies from the four most advanced candidates……Even fewer subjects—32 in the case of a study sponsored by Pfizer Inc. — would need to be infected and develop symptoms in each trial before researchers take an early look at how a shot is doing and see if it could be cleared provisionally, the review found.
