The Scottish government said earlier this week that nine cases had been linked to a single private event with no known travel link.
So far, authorities have been unable to link the English case to a travel history linked to southern Africa, where the strain was first detected, either directly or through contact with another traveler, the people said.
Meanwhile, dozens of new Omicron sequences were being evaluated by health officials, suggesting the number of cases will increase in the coming days. The UK has severely restricted travel to and from 10 southern African countries.
The British Health Safety Agency on Thursday confirmed seven more cases in England, bringing the total number of Omicron cases reported so far to 29. In Scotland, health authorities have discovered 13 infections caused by the new variant. The UKHSA did not respond to a request for comment on the case of community transmission in England.
Nicola Sturgeon, the Scottish Prime Minister, said on Tuesday that what was known about the first cluster of nine cases of Omicron in the country suggested there was already “limited” community transmission of the variant.
Last week, the World Health Organization named the variant as one of “concerns” after a sharp increase in Omicron cases in South Africa. He said on Wednesday that it had been detected in at least 23 countries, adding that he expected that number to increase.
Scientists are alarmed by the variant, fearing that its high number of mutations will allow it to spread faster than the currently dominant Delta variant and bypass immune protection provided by vaccines or a previous infection. Studies are underway to understand this. It is also not yet known whether Omicron is changing the severity of the Covid-19 infection.
A person with knowledge of the English cases added that it had been difficult to trace contacts in some cases, as some of those confirmed to be infected with Omicron left the country shortly thereafter while some also ignored the ‘isolation.
Separate test data, analyzed by government science advisers, gave a first indication that Omicron may be more prevalent in England.
Due to a genetic quirk, Omicron can be detected by some type of PCR test, which is used in about half of all community tests performed.
Omicron lacks one of three coronavirus gene targets – the S gene – analyzed by commercial detection kits, giving epidemiologists insight into its spread without the need for genomic sequencing.
Surveillance data in England showed that the proportion of Covid-19 cases with S gene drop fell from a background level of 0.06% between August and October to around 0.3%, as of November 28 .
However, health officials are reluctant to overinterpret the recent surge, as suspected cases of Omicron may be preferentially brought forward for testing for the S gene.
Mark Woolhouse, professor of infectious disease epidemiology at the University of Edinburgh, said the signal has been found to be “extremely useful” in showing an increase in Omicron cases in South Africa.
“In South Africa they are now detecting many more cases without the S gene since Omicron was first detected,” Woolhouse said. “Based on their experience, we would associate this model with an increase in Omicron. “
The Alpha variant, which was dominant in the UK until mid-May, also had the same genetic quirk.