This phase 3 clinical trial was conducted in the United Kingdom. Adults between 18 and 84 years in a 1:1 ratio receive two intramuscular 5-μg doses of NVX-CoV2373 or placebo administered 21 days apart.

The primary efficacy endpoint was virologically confirmed mild, moderate, or severe SARS-CoV-2 infection with an onset at least 7 days after the second injection in serologically negative participants at baseline.

Results

On September 23, 2021, The New England Journal of Medicine published the results of this clinical trial.

A total of 14,039 were included in the per-protocol efficacy population. 27.9% were 65 years of age or older, and 44.6% had coexisting illnesses. Infections were reported in 10 participants in the vaccine group and 96 in the placebo group, with a symptom onset of at least 7 days after the second injection, for a vaccine efficacy of 89.7% (95% confidence interval [CI], 80.2 to 94.6).

No hospitalizations or deaths were reported among the 10 cases in the vaccine group. Five cases of severe infection were registered, all of which were in the placebo group. A post hoc analysis showed an efficacy of 86.3% (95% CI, 71.3 to 93.5) against the B.1.1.7 (or alpha) variant and 96.4% (95% CI, 73.8 to 99.5) against non-B.1.1.7 variants. Reactogenicity was generally mild and transient. The incidence of serious adverse events was low and similar in the two groups.

Conclusions

A two-dose regimen of the NVX-CoV2373 vaccine administered to adult participants conferred 89.7% protection against SARS-CoV-2 infection and showed high efficacy against the B.1.1.7 variant.