New York, Mar 12 (IANS): US-based biotech company Novavax's Covid-19 vaccine was 96.4 per cent effective against original strain of the virus in a phase-3 trial in the UK, the company has said.

The vaccine, NVX-CoV2373, was found 86.3 per cent effective against the B.1.1.7/501Y.V1 variant circulating in the UK, Novavax said on Thursday.

The study enrolled more than 15,000 participants between 18-84 years of age, including 27 per cent over the age of 65.

The results are expected to bring the approval of the vaccine a step closer as Novavax said that it expects the data to serve as the basis for submission for authorisation to various regulatory agencies worldwide.

The company also announced the complete analysis of its Phase-2b trial taking place in South Africa, with efficacy of 55.4 per cent 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 per cent protection against severe disease, including all hospitalisation and death.

Both studies achieved their statistical success criteria, Novavax said.

"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," Stanley Erck, President and Chief Executive Officer, Novavax, said in a statement.

"Importantly, both studies confirmed efficacy against the variant strains."

Giving details of the UK trial, the company said that in volunteers 65 years of age and older, 10 cases of Covid-19 were observed, with 90 per cent of those cases occurring in the placebo group.

Older adults are among the groups most impacted by the disease and are at high risk of complications from Covid-19.

In the South Africa 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 positive cases - 51 cases in the vaccine group and 96 in the placebo group -- demonstrated an overall efficacy of 48.6 per cent against predominantly variant strains.

The vast majority of cases circulating during the efficacy analysis were due to the B.1.351/501Y.V2 variant circulating in South Africa, the company said, adding that all five cases of severe disease observed in the trial occurred in the placebo group.