Novavax vaccine efficacious against multiple COVID-19 strains

Biotechnology company Novavax has announced final efficacy of 96.4% against mild, moderate and severe disease caused by the original COVID-19 strain in a pivotal Phase 3 trial in the UK of NVX-CoV2373, the company’s vaccine candidate.

The company also announced the complete analysis of its Phase 2b trial taking place 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 hospitalisation and death. Both studies achieved their statistical success criteria.

UK Phase 3 trial

The UK study enrolled more than 15,000 participants between 18 and 84 years of age, including 27% over the age of 65. The primary endpoint of the Phase 3 clinical trial is based on the first occurrence of PCR-confirmed symptomatic (mild, moderate or severe) COVID-19 with onset at least seven days after the second study vaccination in serologically negative (to SARS-CoV-2) adult participants at baseline.

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 UK (post hoc). The primary efficacy endpoint demonstrated an overall vaccine efficacy of 89.7% (95% CI: 80.2, 94.6). 106 cases of COVID-19 were observed, with 10 in the vaccine group and 96 in the placebo group. 10 cases were observed in volunteers 65 years of age and older, with 90% of those cases occurring in the placebo group.

NVX-CoV2373 also proved 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. 14 days after dose 1, vaccine efficacy was 83.4% (95% CI: 73.6, 89.5).

South Africa Phase 2b trial

The South Africa trial was a randomised, observer-blinded, placebo-controlled Phase 2b clinical trial of NVX-CoV2373. One cohort evaluated efficacy, safety and immunogenicity in approximately 2665 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 seven 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 UK and South Africa trials, these analyses showed that the vaccine is well tolerated, with low levels of severe, serious and medically attended adverse events at day 35, balanced between vaccine and placebo groups.

“We are very encouraged by the data showing that NVX-CoV2373 not only provided complete protection against the most severe forms of disease, but also dramatically reduced mild and moderate disease across both trials. Importantly, both studies confirmed efficacy against the variant strains,” said Novavax President and CEO Stanley C Erck.

“With this data in hand, we are even more motivated to advance our vaccine as a potential weapon in the fight to end the suffering caused by COVID-19.”

The Australian Government has agreed to purchase 51 million doses of the Novavax vaccine, subject to approval from the Therapeutic Goods Administration (TGA). The government has also conceded that it may not reach its goal of fully vaccinating all Australians by the end of October, due in part to recent clinical studies which found that AstraZeneca’s vaccine proves more effective when its two doses are administered 12 (rather than four) weeks apart.

Image courtesy of Novavax.

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