British drugmaker AstraZeneca said on Saturday the vaccine it has developed with the University of Oxford appeared to offer only limited protection against mild disease caused by the South African variant of COVID-19, Reuters reports.

A study from South Africa's University of the Witwatersrand and Oxford University showed the vaccine had significantly reduced efficacy against the South African variant, according to a Financial Times report published earlier in the day.

Among coronavirus variants currently most concerning for scientists and public health experts are the so-called British, South African and Brazilian variants, which appear to spread more swiftly than others.

"In this small phase I/II trial, early data has shown limited efficacy against mild disease primarily due to the B.1.351 South African variant," an AstraZeneca spokesman said in response to the FT report.

The newspaper said none of the more than 2,000 trial participants had been hospitalized or died.

"However, we have not been able to properly ascertain its effect against severe disease and hospitalization given that subjects were predominantly young healthy adults," the AstraZeneca spokesman said.

An Oxford University professor said earlier this week that a vaccine against the coronavirus' new mutations should be ready by October.

According to the university's Professor Andrew Pollard, who heads the team working on the vaccine, tweaking the vaccine is a relatively fast process and needs only small trials before the vaccine can be rolled out.

Though studies show that existing vaccines provide some protection against the South African mutation of COVID-19, they have also showed reduced efficacy against it.