Novavax, Inc.’s Phase III trial of NVX–CoV2373 COVID-19 vaccine candidate demonstrated final efficacy of 96.4% against mild, moderate and severe disease caused by the original COVID-19 strain in the UK trial. The company completed analysis of its Phase 2b trial in South Africa, with efficacy of 55.4% among the HIV- negative trial participants in a region where the vast majority of strains are B1.351 escape variants. Across both trials, NVX-CoV2373 demonstrated 100% protection against severe disease, including all hospitalization and death. Both studies achieved their statistical success criteria. This final analyses build on the successful interim results announced in January 2021, adding substantially more COVID-19 cases and statistical power.
 
The UK study enrolled more than 15,000 participants between 18-84 years of age. Efficacy was 96.4% against the original virus strain and 86.3% against the B.1.1.7/501Y.V1 variant circulating in the U.K (post hoc). The primary efficacy endpoint demonstrated an overall vaccine efficacy of 89.7%.
 
The South Africa trial evaluated efficacy, safety and immunogenicity in approximately 2,665 healthy adults in one cohort. The second cohort evaluated safety and immunogenicity in approximately 240 medically stable, HIV-positive adults. A complete analysis of vaccine efficacy demonstrated an overall efficacy of 48.6% against predominantly variant strains. Among HIV-negative participants, 55.4% efficacy was observed.
 
A previously reported initial analysis from the study through 60 days indicated that prior infection with the original COVID-19 strain might not completely protect against subsequent infection by the variant predominantly circulating in South Africa. However, the complete analysis of the South Africa trial indicates that there may be a late protective effect of prior exposure with the original COVID-19 strain. In placebo recipients, at 90 days the illness rate was 7.9% in baseline seronegative individuals, with a rate of 4.4% in baseline seropositive participants.