India's fast-spreading 'double mutant' strain of COVID-19 has arrived in the UK - just as the hard-hit nation emerges from months of lockdown.
B.1.167 was first detected in Maharashtra, a state in western India, in January. It's now the dominant strain in that part of the country, which recently went back into lockdown to curb a fast-growing outbreak. Maharashtra accounts for about a third of the country's deaths to date.
Seventy-seven cases have been found in the UK, Public Health England said on Friday (NZ time). Most - 73 - are in England, which recently lifted some restrictions on movement, and four in Scotland, whose path out of lockdown trails that of their southern neighbours by a couple of weeks.
B.1.167 has two worrying mutations on its spike protein, the bit which it uses to bind to human cells. One is E484Q, similar to the E484K mutation found in the South African (B.1.351) and Brazilian (P.1) strains of SARS-CoV-2, the virus behind COVID-19, and in rare versions of the B.1.1.7 strain out of the UK.
The second mutation is L452R, which also features in two California strains of the virus (B.1.427 and B.1.429) which a local infectious diseases researcher dubbed "the devil".
The fear is their powers combined; the two mutations could mean vaccines have a hard time stopping B.1.167 from infecting people. Some studies have already found the E484K mutation reduces some vaccines' effectiveness.
"These two escape mutations working together could be a lot more problematic than the South African and Brazilian variants who have only got one escape mutation," Paul Hunter, professor in medicine at the University of East Anglia, told The Guardian. "It might be even less controlled by vaccine than the Brazilian and South African variants."
It's not clear yet if the B.1.167 variant is behind the recent surge in cases in India, like B.1.1.7 was in the UK over the Christmas-New Year period.
"We don’t know yet whether it can escape existing vaccines but it has several concerning mutations," said University College London researcher Christina Pagel.
She's warned UK Prime Minister Boris Johnson, who caught the virus last year, to cancel a planned trip to India this month. There have been reports of people catching COVID-19 twice.
Johnson himself earlier this week warned the UK would "inevitably" see rising case numbers and deaths as a result of opening up, but has previously said the course was "irreversible".