Analyses show wide efficacy gap for Novavax vaccine in UK, South Africa trials

Novavax shares rose as much as 22% after-hours on Thursday after the company said its coronavirus vaccine candidate NVX–CoV2373 showed nearly 90% efficacy overall at the final analysis of a Phase III UK-based trial, confirming interim results released in January. The latest analysis was calculated on 106 cases of symptomatic COVID-19 that occurred after the second dose, with 10 cases observed in the vaccine group and 96 in the placebo arm.

Novavax stated it expects the data will form the basis of global regulatory filings, while chief medical officer Filip Dubovsky said the company is planning to seek UK authorisation for NVX–CoV2373 early in the second quarter. The protein-based vaccine candidate was developed using its recombinant nanoparticle technology to generate antigen derived from the SARS-CoV-2 spike and is enhanced with the company's Matrix-M adjuvant.

Protection against severe disease

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

The final analysis showed that NVX–CoV2373 was 89.7% effective overall, with efficacy rates of 96.4% and 86.3%, respectively, against the original strain of SARS-CoV-2 and the B.1.1.7 variant first identified in the UK. There were 10 cases of COVID-19 among participants 65 years and older, with nine of those occurring in the placebo group. Meanwhile, among the five study volunteers who developed severe disease, all of them were in the placebo arm, and four of these infections were caused by the B.1.1.7 variant. Novavax also said its vaccine appeared to work well even after one dose, with efficacy estimated to be 83.4% at 14 days after the first jab.

Less potent in smaller South Africa trial

The company also provided a complete analysis from a Phase IIb trial conducted in South Africa, where one cohort evaluated NVX–CoV2373 in approximately 2665 healthy adults, while a second included 240 medically stable, HIV-positive adult patients. Novavax said the analysis was based on 147 cases of COVID-19, including 51 cases in the vaccine group and 96 for placebo, for an overall efficacy rate of 48.6% "against predominantly variant strains," the vast majority of which were the B.1.351 variant circulating in South Africa. When HIV-positive participants were excluded from the mix, the vaccine was found to be 55.4% effective, although that is below the 60% rate reported at the interim analysis in January. The trial also had five severe cases, with all of them occurring in the placebo group as well.

The company said NVX–CoV2373 was well-tolerated in both the UK and South Africa studies, with "low levels" of severe, serious and medically attended adverse events at day 35 that were balanced between the vaccine and placebo groups.

Meanwhile, Novavax also noted that the complete analysis of the South Africa trial suggests there may be a "late protective effect" to B.1.351 that comes from prior exposure with the original strain of the virus. An earlier analysis done through to 60 days had indicated that prior infection might not completely protect against subsequent infection with B.1.351. However, in the complete analysis, the illness rate at 90 days was 7.9% for placebo recipients who were seronegative at baseline, whereas the rate was 4.4% for those who were baseline seropositive.

US data readout in early April

Last month, Novavax said it completed enrollment of 30,000 volunteers into the Phase III PREVENT-19 trial of NVX-CoV2373 being run in the US and Mexico. The trial, which began in December, will assess two intramuscular injections of the vaccine, administered 21 days apart, in people aged 18 years and older, including 13% who are 65-plus. A data readout is expected in early April.

CEO Stanley Erck recently suggested the vaccine could be cleared in the US as soon as May if regulators there decide the UK data is enough to make a decision, but that it would take a couple months longer if they insist on seeing data from the US trial first.

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