UK public health officials on Friday upgraded the status of one of the coronavirus variants first identified in India following growing scientific evidence that it is more transmissible than others in circulation.

Although Public Health England said there was “currently insufficient evidence” to show the B.1.617.2 mutation caused more severe illness or rendered vaccines less effective, the strain was reclassified from a “variant under investigation” to a “variant of concern”.

The change in status will trigger surge testing in areas where the identification of a case triggers particular concern, meaning both symptomatic and asymptomatic individuals are tested for the virus.

Cases of B.1.617.2 have increased to 520 from 202 over the past week, PHE added, with almost half the cases related to travel or contact with a traveller.

The variant has been blamed by some for the surge in infections in India, which reported more than 414,000 confirmed cases on Thursday alone.

UK prime minister Boris Johnson said on Friday that the government was being “absolutely ruthless” in tracking the new variant. He added that he “couldn’t see any reason now” to delay plans to lift coronavirus restrictions.

B.1.617.2 has shown a much sharper rate of spread than other imported variants of concern in the UK, including B.1.351 from South Africa and P.1 from Brazil, both of which have either plateaued or declined.

Chart showing that the Indian variant subtype B.1.617.2 is growing faster in the UK than other imported variants

Scientists have also identified two other slightly different mutations related to the original variant first discovered in India — called B.1.617.1 and B.1.617.3.

But it is the B.1.617.2 variant that is causing the greatest concern in the UK. PHE said the cases discovered so far were spread across the country, but with the majority in two areas — the North West (predominantly Bolton) and London. “This is where we are seeing the greatest transmission,” PHE said.

Officials are now watching closely to see whether it spreads faster than the so-called Kent variant — B.1.1.7 — which was first discovered in the UK.

“The big question will be whether it outcompetes B.1.1.7 and starts to spread under the current restrictions, which have largely been holding B.1.1.7 at bay,” said one senior public health official.

B.1.617.2, which was first detected in the UK in April, is on almost exactly the same path as B.1.1.7 was 40 days into its spread.

Chart showing that B.1.617.2 is following the same path as B.1.1.7 did in terms of its growing share of sequenced cases

“B.1.1.7 is really fit so we don’t know how these variants are actually going to play out when they’re in competition with another,” said Muge Cevik, a clinician and researcher in virology at the university of St Andrews.

B.1.1.7 was growing during a time when overall cases were on the rise, whereas B.1.617.2 is spreading at a time when overall numbers are falling, which has led some to fear that the current lockdown measures are not having the same impact.

Chart showing that Cases of B.1.617.2 are rising at a time when the national trend has been downwards

With PHE saying half the cases discovered so far were related to travel, scientists remain concerned over the extent of community transmission, believed to be much more concerning and difficult to get under control.

“The critical question remains, how much of these B.1.617.2 cases are imported (and therefore reflecting the epidemiology in India) vs how many were acquired here?,” said John Edmunds, a professor of infectious modelling at the London School of Hygiene and Tropical Medicine.

In a positive twist, the B.1.617.2 variant does not have a particularly concerning mutation — called E484Q — that is associated with variants being able to resist vaccine induced immunity. This is despite the fact that its parent lineage does have the mutation.

Sharon Peacock, a professor of public health and microbiology at the University of Cambridge, described this as a “promising sign” that the existing crop of vaccines will protect against the variant, even if it is more transmissible.

“The current evidence — and it’s very thin — is that the variant won’t have significant immune evasion compared to the South African variant,” she said.

The limited laboratory work to date conducted at Cambridge university indicates that vaccines do work, at least to some extent, at protecting against the most concerning mutations found in the B.1.617 variants.

“Right now the most important thing is that the vaccines are working against this variant,” Cevik said.