The Oxford/AstraZeneca vaccine may not significantly reduce the number of cases but will protect against deaths and severe disease amid the spread of the South African variant, the lead researcher behind the jab has said.

Preliminary research has suggested the vaccine offers minimal protection against mild disease caused by the variant.

But AstraZeneca said it believes the jab will still protect against severe disease caused by the mutation.

The study, first reported by the Financial Times, involved some 2,000 people, most of whom were young and healthy.

On Sunday, lead researcher in the Oxford team Professor Sarah Gilbert said the current vaccines “have a reduction in efficacy against some of the variant viruses”.

However, she added: “What that is looking like is that we may not be reducing the total number of cases but there’s still protection in that case against deaths, hospitalisations and severe disease.”

She told the BBC’s Andrew Marr Show: “Maybe we won’t be reducing the number of cases as much, but we still won’t be seeing the deaths, hospitalisations and severe disease.

“That’s really important for healthcare systems, even if we are having mild and asymptomatic infections, to prevent people going into hospital with Covid would have a major effect.”

The study also appeared to show that the South African mutations will allow for ongoing transmission of the virus in vaccinated populations.

Oxford University said the study did not assess protection against moderate to severe disease, hospital admission or death because the target population were at such low risk.

However, it also said that analysis being submitted showed the vaccine had high efficacy against the original coronavirus strain in South Africa.

A spokesperson for AstraZeneca said: “We do believe our vaccine will still protect against severe disease, as neutralising antibody activity is equivalent to other Covid-19 vaccines that have demonstrated activity against more severe disease, particularly when the dosing interval is optimised to eight to 12 weeks.”

The spokesperson added that other immune responses, such as T cell responses, may have a role in protecting against disease, and initial data suggests these may stay the same with the variant.

Professor Robin Shattock, who is leading Covid-19 vaccine research at Imperial College London, urged caution about the study’s early findings.

He told BBC Breakfast: “It’s a very small study with just over 2,000 people and it’s not published so we can only judge it from the press release and press coverage. But it is concerning to some extent that we’re seeing that it’s not effective against mild or moderate disease.”

Prof Gilbert said her team currently has “a version with the South African spike sequence in the works” with the hopes it will be ready to administer by the autumn.

She went on: “It’s not quite ready to vaccinate people with yet, but, as all of the developers are using platform technologies, these are ways of making a vaccine that are very quick to adapt.”

Andrew Pollard, professor of paediatric infection and immunity, and chief investigator on the Oxford vaccine trial, said: “This study confirms that the pandemic coronavirus will find ways to continue to spread in vaccinated populations, as expected, but, taken with the promising results from other studies in South Africa using a similar viral vector, vaccines may continue to ease the toll on healthcare systems by preventing severe disease.”

The South African variant study comes after research released on Friday indicated that the Oxford/AstraZeneca jab is effective at fighting the new UK coronavirus variant.