Novavax confirms high efficacy against original, variant COVID-19 strains in UK, South Africa trials

The primary endpoint of the U.K. Phase 3 clinical trial is based on the first occurrence of PCR-confirmed symptomatic (mild, moderate or severe) COVID-19 with onset at least 7 days after the second study vaccination in serologically negative (to SARS-CoV-2) adult participants at baseline.

The study enrolled more than 15,000 participants between 18-84 years of age, including 27% over the age of 65.

Efficacy was 96.4% (95% CI: 73.8, 99.5) against the original virus strain and 86.3% (95% CI: 71.3, 93.5) 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% (95% CI: 80.2, 94.6). 106 cases were observed, with 10 in the vaccine group and 96 in the placebo group. NVX-CoV2373 was effective against severe disease: five severe cases were observed in the study, and all occurred in the placebo group. Four of the five severe cases were attributed to the B.1.1.7/501Y.V1 variant. Fourteen days after dose 1, vaccine efficacy was 83.4% (95% CI: 73.6, 89.5).

In volunteers 65 years of age and older, 10 cases of COVID-19 were observed, with 90% of those cases occurring in the placebo group. Older adults are among the groups most impacted by the disease and are at high risk of complications from COVID-19.

"Novavax expects the data to serve as the basis for submission for authorization to various regulatory agencies worldwide" the release stated

The South Africa trial was a randomized, observer-blinded, placebo-controlled Phase 2b clinical trial of NVX-CoV2373. One cohort evaluated efficacy, safety and immunogenicity in approximately 2,665 healthy adults. The second cohort evaluated safety and immunogenicity in approximately 240 medically stable, HIV-positive adults.

A complete analysis of vaccine efficacy among 147 PCR-positive cases (51 cases in the vaccine group and 96 in the placebo group) demonstrated an overall efficacy of 48.6% against predominantly variant strains (95% CI: 28.4, 63.1). The vast majority of cases circulating during the efficacy analysis were due to the B.1.351/501Y.V2 variant circulating in South Africa. All five cases of severe disease observed in the trial occurred in the placebo group. Among HIV-negative participants, 55.4% efficacy was observed (95% CI: 35.9, 68.9). The complete analysis shows that vaccine-induced protection began 14 days after dose 1 (42.7% 95% CI: 25.0, 56.3), although increased efficacy was observed 7 days after dose 2, the primary endpoint for the study.

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.

In both the U.K. and South Africa trials, these analyses showed that the vaccine is well-tolerated, with low levels of severe, serious (SAEs) and medically attended adverse events at day 35, balanced between vaccine and placebo groups.