It is too early to judge the full extent of the strain of coronavirus, which was first identified in the UK on August 18, and it has not been classed as a variant of concern.
But enough unlinked cases of BA.2.86 have been detected in different parts of the country to suggest it is circulating among the community.
An outbreak of Covid-19 in a care home in Norfolk at the end of August saw 33 out of 38 residents test positive for the virus, along with 12 members of staff, according to the UK Health Security Agency (UKHSA).
One resident needed hospital treatment but no deaths due to Covid-19 have been reported.
Laboratory tests later showed that 22 residents had the BA.2.86 variant, along with six members of staff.
The outbreak is “an early indicator” that the variant may be sufficiently transmissible to have an impact in close contact settings, the UKHSA said – though it is “too early” to draw any conclusions about how BA.2.86 will behave in the wider UK population.
Some 29 of the 33 residents at the care home who tested positive for Covid-19 have now recovered, along with all members of staff, the UKHSA added.
Specialists have been working with Norfolk County Council to offer infection control advice and support.
Dr Renu Bindra, UKHSA incident director, said that while BA.2.86 has a “significant number of mutations” compared with other variants circulating among the population, the data so far is “too limited to draw firm conclusions” about the impact this will have on the transmissibility or severity of the virus.
She added: “UKHSA scientists are working with international partners to culture the samples and analyse the evidence as it becomes available.
“However, it is likely to be some time before we have enough data to make a confident assessment.
“It is clear that there is some degree of widespread community transmission, both in the UK and globally, and we are working to ascertain the full extent of this.
“In the meantime, it remains vital that all those eligible come forward to receive their autumn vaccine as soon as it is offered to them.”
The rollout of the latest Covid-19 vaccine booster has been brought forward from October to September as a precautionary measure against BA.2.86.
The booster programme will begin in England on September 11, with jabs offered first to residents of adult care homes and clinically vulnerable people.
The rollout will then be extended to everyone in the UK aged 65 and over.
There are no longer any official estimates of the prevalence of Covid-19 among the UK population, meaning it is impossible to get a full and reliable picture of the spread of the virus.
Testing for Covid-19 has also been scaled back sharply, so there is not as much data available for analysis.
In the absence of more comprehensive figures, the number of people in hospital with coronavirus can offer a guide to changes in the level of Covid-19 in circulation.
Some 2,879 patients in England had tested positive for the virus as of September 3, up 13% on the previous week and the highest number since May 26, according to NHS data.
This is still well below the level reached during last winter, when the number was nearly 10,000 people, and even further below the peaks seen in the first year of the pandemic.
The current rise in patients testing positive was under way several weeks before the discovery of the BA.2.86 variant.
Other factors, such as more social mixing in homes or among crowds at large indoor venues, may have contributed to the increase.