A A new, more infectious strain of Covid is spreading across the UK but appears less likely to cause symptoms, scientists say.
The Delta AY.4.2 branch, which was designated the study variant, represented about 12% of the samples collected in an ongoing study that ran through November 5.
Experts believe it could be 10% more infectious than other Delta variants. However, preprinted research from the latest cycle of the REACT-1 study suggested it was less likely to cause symptoms.
Two-thirds (66.7%) of people with variant AY.4.2 in the study had symptoms, compared to 76.4% of those with its parent Delta, AY.4.
One-third of people with the variant reported the classic Covid symptoms of a persistent cough, fever, or loss or change in taste and smell.
AY.4.2 does not appear to make the vaccines less effective than the original Delta strain.
“Right now it appears to be around 10% more infectious than the other delta variants, although I’m not sure why yet,” said Professor Paul Hunter, professor of medicine at the University of East Anglia.
Scientists say it’s too early to say for sure whether the new subvariant is less likely to make people sick.
Other factors could be at play, such as a greater number of cases recorded in those who already have partial immunity.
“If this association is confirmed, there are several possibilities, one of which is that the variant is indeed less virulent or is more likely to cause infections in partially immune people,” said Professor Hunter, who added that further research needed to be completed.
REACT program director Professor Paul Elliott told Journal I that if the association is confirmed, it could give the variant a ‘transmission advantage’ because fewer people will know they have Covid if they do not present no symptoms.