Novavax Inc's Covid-19 vaccine had efficacy of 51 per cent against infections caused by the South African variant among people who were HIV negative, and 43pc in a group that included people who were HIV positive, according to a new analysis.

The variant, known as B.1.351, carries mutations that threaten the efficacy of Covid-19 vaccines, several studies have shown. Most vaccine makers, including Novavax, are testing versions of their vaccines to protect against emerging variants.

The Novavax post-hoc analysis was published in the New England Journal of Medicine along with full data from the company's trial in South Africa, which included nearly 2,700 volunteers who had not been previously infected with the coronavirus.