A Study to Evaluate the Safety and Immunogenicity of an (Omicron Subvariant) COVID-19 Vaccine Booster Dose in Previously Vaccinated Participants and Unvaccinated Participants.

Novavax, Inc. developed a recombinant prototype COVID-19 vaccine constructed from the full-length ancestral (Wuhan) SARS CoV-2 S glycoprotein (GP) adjuvanted with the saponin-based Matrix-M adjuvant (NVX-CoV2373). Subsequently, the SARS CoV 2 Omicron variant and subvariants emerged with enhanced transmissibility and the most significant number of mutations in any strain to date. Current evidence demonstrates that variant strain mutations such as those in the Omicron XBB.1.5 sublineage confer the ability to evade both natural and vaccine-induced neutralizing antibodies. Part 1 of the study aims to investigate the safety and immunogenicity of the Novavax XBB.1.5 SARS-CoV-2 rS vaccine (NVX-CoV2601) adjuvanted with Matrix-M in previously COVID-19 mRNA vaccinated participants to determine if it induces superior antibody responses compared to a historical control of the prototype vaccine (original Wuhan strain), NVX-CoV2373. Part 2 of the study aims to investigate the safety and immunogenicity of 1 dose of NVX CoV2601 in baseline SARS-CoV-2 seropositive COVID-19 vaccine naïve participants to determine if it induces non-inferior antibody responses compared to 1 booster dose of NVX-CoV2601 in previously COVID-19 mRNA vaccinated individuals participating in Part 1. Part 1: Approximately 330 previously mRNA COVID-19 vaccinated participants will receive a booster dose of XBB.1.5 Omicron subvariant vaccine (NVX-CoV2601) on Day 0. Immunogenicity and 28-day safety data will be used for an interim analysis, while participants remain on the study for immunogenicity and safety data collection up to Day 180 post-vaccination. Part 2: After completion of Part 1, approximately 330 unvaccinated participants with a clinical history of COVID-19-like disease during the previous year will receive a booster dose of NVX-CoV2601 on Day 0. Immunogenicity and 28-day safety data will be used for an interim analysis, while participants remain on the study for immunogenicity and safety data collection up to Day 180 post vaccination.