Novavax Covid-19 vaccine nearly 90 per cent effective, less so in South Africa

Novavax's Covid-19 vaccine candidate achieved a very high efficacy, the results of the company's late-stage clinical trials showed.

However, its success against the new novel coronavirus strain recently detected in South Africa was lower, albeit still substantial.

The news sent stock in the US biotechnology outfit 26.93% higher in after-hours trading in New York to $170.1.

Interim results from the 15,000-person strong trial in the UK showed the vaccine achieved an efficacy rate of 89.3%, which is well above what is typically seen in vaccines.

Critically, the vaccine was effective against the new B.1.1.7 virus strain first detected in the UK.

London already has a deal with the firm for 100m doses of the vaccine which mimics the virus's so-called spike 'protein'.

However, a second trial conducted in parallel among 4,400 volunteers in South African showed a drop in the vaccine's efficacy to 60%, which is still comfortably above the 50% threshold that US health officials require for marketing approval.

The reason for the lower efficacy was the new virus strain that is already prevalent in that African country, known as B.1.351, with most of the infections recorded during the trial being caused by it.

Furthermore, when HIV positive patients - who are a minority - were included in the tally, then the overall efficacy figure was even lower, at 49.4%.

Fortunately, Novavax had already begun work on a new vaccine designed to counter the new virus strains.