With GSK plc’s Arexvy approved in the U.S. as the first respiratory syncytial virus (RSV) vaccine, several other developers are lining up for what in five years could be a $10 billion market. Their aim is to provide lasting protection for those most susceptible to the endemic virus, particularly young children and those older than 60. Behind GSK is Pfizer Inc. with PF-06928316, which has a U.S. FDA PDUFA date set for this month, and Sanofi SA’s nirsevimab, for which FDA action is expected in the third quarter.