On Nov. 9, 2022, Novavax announced that the Medicines and Healthcare products Regulatory Agency (MHRA) in the United Kingdom had expanded the conditional marketing authorization for Nuvaxovid (NVX-CoV2373) COVID-19 vaccine as a homologous and heterologous booster dose after the primary series of Nuvaxovid (six months) or of an mRNA or adenoviral vector vaccine for active immunization to prevent coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in adults aged 18 and older.

The MHRA decision was based on data from Novavax’ Phase 2 trial conducted in the U.S. and Australia (1,283 participants), from a separate Phase 2 trial conducted in South Africa (4,404 participants), and from the U.K.-sponsored COV-BOOST trial (2,878 participants). As part of the Phase 2 trials, a single booster dose of Nuvaxovid was administered to healthy adult participants approximately six months after their primary two-dose vaccination series of Nuvaxovid. The third dose produced increased immune responses against the original ancestral strain of SARS-CoV-2 comparable to or exceeding levels associated with protection in Phase 3 clinical trials. In the COV-BOOST trial, Nuvaxovid increased antibody titers when used as a heterologous third booster dose after a primary two-dose vaccination series of an mRNA vaccine or adenoviral vector vaccine.

In the Novavax-sponsored trials, following the booster, local and systemic reactions had a median duration of approximately two days. Adverse reactions were usually mild to moderate in severity. Safety reporting of reactogenicity events showed an increasing incidence across all three doses of Nuvaxovid. Medically attended adverse events (AE), potentially immune-mediated medical conditions, and severe AEs occurred infrequently following the booster dose and were balanced between vaccine and placebo groups.