British health authority monitors Delta subvariant
Anew subvariant of the Delta strain of Covid-19 is spreading in the UK.
AY.4.2 is being monitored by scientists, who believe it may be more transmissible than the variant first detected in India last year. That means it could be the most infectious strain to date.
Q
What is a subvariant and how did this one emerge?
A
All viruses change over time. Research by the University of Bath and University of Edinburgh found the virus that causes Covid-19 mutates about once a week, which is about 50 per cent higher than previous estimates.
Most mutations are harmless glitches that bring no benefit to the virus, but sometimes they allow the virus to spread more easily.
Delta is estimated to be about twice as transmissible as the original strain.
Because it spreads faster, it became the dominant variant around the world. But it has continued to mutate, creating a new subvariant.
How is the Delta subvariant different?
It includes two mutations, Y145H and A222V, to the spike protein of the virus, which it uses to latch on to cells.
The mutations have been reported in other variants.
“Most Sars-CoV-2 mutations have independently emerged many times in unrelated strains,” said Francois Balloux, head of the University College London Genetics Institute.
“Both the spike Y145H and A222V mutations have been found in various other SaraCoV-2 lineages since the beginning of the pandemic, but have remained at low frequency until now.”
Strains that carried the mutations were first detected in April last year, he said.
“The A222V was found in the B.1.177 lineage that swept Europe in the summer of 2020, but careful follow-up analysis pointed to the lineage probably having no inherent transmissibility advantage and that its spread was most probably caused by demographic processes,” he said.
Neither of the mutations are found in any variant of concern, which are strains considered inherently more severe or transmissible by the World Health Organisation.
“But we have learnt that mutations can have different, sometimes unexpected, effects in different strains,” Prof Balloux said.
How common is the subvariant in the UK?
It accounts for about 6 per cent of cases in the country. A National Health Service
document published last week showed the subvariant was one of four being monitored by the UK Health Security Agency.
How common is it outside the UK?
It is rare. There have been only three cases detected in the US so far, Prof Balloux said.
In Denmark, which carries out regular genomic monitoring, the subvariant previously accounted for 2 per cent of cases but has since faded.
Could the subvariant be more transmissible than Delta?
Prof Balloux said the increase in cases of the subvariant suggested it could be about 10 per cent more transmissible than the original Delta strain.
“The emergence of yet another more transmissible strain would be suboptimal, though this is not a situation comparable to the emergence of Alpha and Delta that were far more transmissible than any strain in circulation at the time,” he said.
“Here we are dealing with a potentially small increase in transmissibility that would not have a comparable impact on the pandemic.”
Work is also under way to test whether the subvariant is more resistant to vaccines, Prof Balloux said.