Public health experts have recommended one version of the Indian coronavirus variant be made a “variant of concern” in the UK, the BBC has been told.
Public Health England (PHE) is tracking B.1.617.2 which appears to spread more quickly than two other identified subtypes of the Indian variant.
Scientists also believe it is at least as transmissible as the variant detected in Kent last year.
A spokesman for PHE said it would not comment on leaked data.
There is no evidence this version of the Indian variant is resistant to current vaccines, a source has told the BBC.
It is believed more than 500 cases of B.1.617.2 have now been detected across England with the highest levels in London and the North West.
That would represent a sharp rise from the 202 cases officially recorded by PHE in the UK as of 28 April – but still a small proportion of overall cases.
It is not known how many of the current infections in the UK can be linked to international travel.
However, it is thought there has already been some evidence of “significant” community transmission, mainly linked to workplaces and religious gatherings.
In one cluster at a care home, 14 elderly residents who had all been vaccinated, were infected with the variant, the source said. A number needed hospital treatment, but not for severe disease, and it is thought all have now recovered.
All current vaccines are thought to offer some degree of protection against variants but can never completely stop all Covid infections, especially among vulnerable or elderly people.