Results of the Novavax Covid-19 vaccine trial in the UK and South Africa have confirmed high levels of efficacy against the original and variant Covid-19, says the University of the Witwatersrand (Wits).

Wits Vaccines and Infectious Diseases Analytics research unit executive director Professor Shabir Madhi leads the Novavax Covid-19 vaccine trial in South Africa.

An updated analysis of the Novavax vaccine trial in South Africa shows vaccine efficacy of 55.4% against mainly mild Covid-19 among human immunodeficiency virus- (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 owing to the B.1.351 variant dominating in South Africa was 100%, with all Covid-19 hospitalisation and deaths having occurred in the placebo group.

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 offers 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 hospitalisation 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, owing 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 UK.

Wits reports that 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 South African 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,” says Novavax president and CEO Stanley Erck.

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

One cohort evaluated efficacy, safety and immunogenicity in about 2 665 healthy adults.

The second cohort evaluated safety and immunogenicity in about 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 owing 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 the first dose, although increased efficacy was observed seven days after the second dose, 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 that, as a benefit to the study volunteers, Wits plans on offering 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.