The variant of coronavirus first detected in India could still infect people vaccinated against the disease, scientists said.
Prof Danny Altmann of Imperial College London said new variants should be treated with caution because vulnerable people could be “caught out” if the strain is able to evade the immune system.
His warning on Monday comes amid growing calls for India to be added to the UK’s red list of travel-ban countries.
Boris Johnson on Monday cancelled his upcoming trip to India when the pandemic situation worsened on the subcontinent.
A scaled-down trip had been due to take place next week but the tour has now been scrapped entirely.
A total of 77 cases of the variant known as B.1.167, first identified in India, was reported in the UK up to April 14.
Health authorities labelled the strain as a “variant under investigation” but this could progress to a “variant of concern” if it is found to spread more easily or to evade vaccines.
Prof Altmann said there was still a large proportion of the UK population who had yet to receive a second dose of a Covid-19 vaccine, while others were still waiting for their first.
“We are still vulnerable, and some people in our population are still vulnerable. What I mean by that is the Indian variant, for example, certainly has a mutation like the ones that evade the best neutralising antibodies,” he told ITV.
“If you have a population where at least half of us have had zero or one dose of vaccine, some won’t have made a very good response to the vaccine, because perhaps they are very old or obese or unwell.
“We still have a very large vulnerable population who can still be caught out by variants like this.”
The variant contains a “double mutation” in the spike protein that could make it more infectious – although scientists were still looking for firm evidence of such.
The variants first identified in south-east England, South Africa and Brazil contain only one mutation.
Prof Andrew Hayward of University College London said India should be added to Britain’s red list of countries while the new strain is investigated.
"The evidence of increased transmissibility and escape from immunity is circumstantial but it is going to take a number of weeks for that variant to be firmed up," he told BBC's Radio 4 Today programme.
“What we have is an unknown level of risk … my own preference is to err on the side of caution and act sooner rather than later, but ultimately that will be a political decision to place India on the red list.”
Dr Susan Hopkins, chief medical adviser for NHS Test and Trace, said the UK did not yet have enough data to determine whether India should be put on the list.
Prime Minister Boris Johnson said the decision was out of his hands.
“The red list is very much a matter for the independent UK Health Security Agency. They will have to take that decision,” he said.
An expanded red list including India means only UK citizens could return from the country and those doing so must pay to quarantine in a government-approved hotel for 10 days.
Dr Jeffrey Barrett, director of the Covid-19 Genomics Initiative at the Wellcome Sanger Institute, was optimistic about the risk posed by the Indian variant.
He said the variant was probably not as infectious as the B.1.1.7 strain first identified in Kent, southern England.
“In terms of spread, clearly this variant has increased in frequency in India around the same time as their very large and tragic recent wave,” he said.
“But I just don’t think we know yet whether there’s a cause and effect relationship – is this variant driving that spread? Or is it happening at the same time perhaps due to a coincidence?
“And one thing to note is that there were some sequences of this variant B.1.167 seen late last year. And so, in some sense, if it really is driving this wave, the fuse has been burning for quite a long time, which would make it look probably less transmissible than B.1.1.7.”
India’s most recent wave of coronavirus is devastating, with a record 256.947 cases and a record 1,757 deaths reported on Monday.
India’s capital region of Delhi will enter a six-day lockdown on Monday night as the country’s health system crumbles under the weight of new infections.
Fewer than 100 critical care beds were available in the city of New Delhi, with a population of more than 20 million people, Chief Minister Arvind Kejriwal said on Sunday.
