Novavax, Inc., the American vaccine development company, has been developing a recombinant protein nanoparticle COVID-19 vaccine currently termed NVX-CoV2373. The full-length spike protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is created in a baculovirus vector, which is then inserted into a lipid nanoparticle around 50 nm in diameter.