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British and international authorities are closely monitoring a subtype of the Delta variant that is causing a growing number of infections in the United Kingdom.
This descendant of the Delta variant, known as AY.4.2, accounted for an estimated 6% of cases in the week of September 27 -- the last week with complete sequencing data -- and is "on an increasing trajectory," a report by the UK Health Security Agency said.
Little is known about AY.4.2. Some experts have suggested it could be slightly more transmissible than the original Delta variant, though that has not yet been confirmed. While it accounts for a growing number of infections, it is not yet classified in the UK as a "variant of concern." It currently remains rare beyond Britain, with a small number of cases being recorded in Denmark and the US, expert Francois Balloux told the Science Media Center (SMC) on Tuesday.
"As AY.4.2 is still at fairly low frequency, a 10% increase its transmissibility could have caused only a small number of additional cases. As such it hasn't been driving the recent increase in case numbers in the UK," Balloux, Professor of Computational Systems Biology and Director at the UCL Genetics Institute, told the SMC.
