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Novavax Covid-19 vaccine trial results in SA and UK confirm high levels of efficacy

- Wits University

Results of the Novavax Covid-19 vaccine trial in SA and UK have confirmed high levels of efficacy against the original and variant Covid-19.

The results show 100% protection against severe disease in both the SA and the UK trials.

Results announced today also showed efficacy against variants circulating in SA and the UK.

An updated analysis of the Novavax vaccine trial in South Africa shows vaccine efficacy of 55.4% against mainly mild Covid-19 among HIV-negative trial participants, in a country where the vast majority of strains are B.1.351 escape variants.

In addition, protection against severe disease due to the B.1.351 variant dominating in South Africa was 100%, with all Covid-19 hospitalization and deaths having occurred in the placebo group.

Professor Shabir Madhi, Executive Director of the Wits Vaccines and Infectious Diseases Analytics (VIDA) Research Unit, leads the Novavax Covid-19 vaccine trial in South Africa.

“The results from the South African trial reinforce that, even with the evolution of the SARS-CoV-2 virus developing mutations in an attempt to evade immune responses induced following natural infection by ancestry virus, the first generation of Covid-19 vaccines still offer great potential especially in mitigating severe disease and death from Covid-19.

This was evident in South Africa where all the cases of Covid-19 hospitalization and death occurred in the unvaccinated control group. This despite the effectiveness of the first generation Covid-19 vaccines being variably affected in reducing the risk of mild Covid-19 caused by the B.1.351 variant, due to the variant being relatively resistant to the antibody induced by all Covid-19 vaccines.”

In a separate study of the Novavax Covid-19 vaccine in the UK, 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).

These updated final analyses build on the successful interim results announced in January 2021, adding substantially more Covid-19 cases and statistical power in both studies.

In both the SA and UK 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 Stanley C. Erck, President and Chief Executive Officer, Novavax.

About the South African Novavax Covid-19 vaccine trial

The South Africa trial was a randomized, observer-blinded, placebo-controlled Phase 2b clinical trial.

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% with majority of illness being mild or moderate.

The vast majority of cases 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.

The complete analysis shows that vaccine-induced protection began 14 days after dose 1, 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.

Madhi says: “As a benefit to the study volunteers, without whose selfless contribution this important study would not have been possible, we now plan to offer all of them the Novavax vaccine so they can be protected immediately against mild – and more importantly – severe Covid-19 being caused by the B.1.351 variant.”