On May 31, 2022, Novavax announced the initiation of its Phase 3 strain change trial to determine if its Omicron variant specific vaccine, NVX-CoV2515 (Omicron BA.1 strain), induced superior antibody responses against the Omicron variant compared to its Wuhan prototype vaccine, NVX-CoV2373, in participants who had received either a primary (two doses) or booster (three doses) series of an mRNA vaccine.

The trial also sought to determine the antibody responses to a bivalent vaccine, containing both NVX-CoV2373 and NVX-CoV2515, administered in participants who have received a booster series of an mRNA vaccine.