Deadly blazes are upending life in wine country, threatening business for vintners and wine-grape producers and creating hazardous conditions for workers responsible for harvesting grapes.

Just 150 or so of the 30,000 or more subjects enrolled in U.S. trials conducted by Pfizer, AstraZeneca, Moderna and Johnson & Johnson 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.