England will bring forward the start of its autumn flu and COVID-19 vaccination programs as a precautionary measure after the identification of highly mutated COVID variant BA.2.86, which has been found in Britain.

Scientists have said BA.2.86, an offshoot of the Omicron variant, was unlikely to cause a devastating wave of severe disease and death, given immune defenses built up worldwide from vaccination and prior infection.

However, Britain's health ministry said annual vaccination programs for older and at-risk groups would start a few weeks earlier than planned in light of the variant.

"As our world-leading scientists gather more information on the BA.2.86 variant, it makes sense to bring forward the vaccination program," said junior health minister Maria Caulfield in a statement.

The variant was first detected in Britain on August 18 and vaccinations will start on September 11, with care home residents and people at highest risk to receive the shots first.

It is not currently categorized as a "variant of concern" in Britain, and the health ministry said there was no change to wider public health advice.

The variant was first spotted in Denmark on July 24 after the virus infecting a patient at risk of becoming severely ill was sequenced. It has since been detected in other symptomatic patients, in routine airport screening, and in wastewater samples in a handful of countries.

England has been without coronavirus restrictions since February 2022, and UK Health Security Agency Chief Executive Jenny Harries said new variants were expected as a result of living with COVID-19.

"There is limited information available at present on BA.2.86 so the potential impact of this particular variant is difficult to estimate," Harries said in the statement.

"As with all emergent and circulating COVID-19 variants ... we will continue to monitor BA.2.86 and to advise government and the public as we learn more."