Helix launched the study when researchers spotted a drop in the prevalence of the Alpha variant, a contagious strain first spotted in the U.K. that had quickly become the dominant variant in that country and the U.S. The researchers discovered the drop in relative frequency of the Alpha variant in their spot checks of strains circulating in the U.S. was due to a rapid increase in two other variants: the Gamma variant, first spotted in Brazil, and the Delta variant. The Gamma variant may be slightly better than the original strain at outmaneuvering the vaccines, researchers say. "It looks like both of them are going to slowly push out Alpha," says Lee, whose study has not yet been peer-reviewed but has been posted on a pre-print server.