An increase in Covid cases across the UK is likely being driven by BA.4 and BA.5 - two Omicron subvariants that may have evolved to target the lungs, experts believe.
BA.4 and BA.5 are newer Omicron strains that were recently classified as “variants of concern”, after analysis found both were likely to have a “growth advantage” over BA.2.
They are now thought to be the most dominant variants in much of the UK and the Office for National Statistics (ONS) said the latest rise in cases was “likely caused by infections compatible" with BA.4 and BA.5.
A total of 1.4 million people in private households are estimated to have had the virus the week starting July, up 43% from the previous week, according to the ONS.
The number of people in hospital with Covid is also showing signs of an upwards trend, although the number of registered deaths involving coronavirus remains low. According to data from University of Tokyo's Kei Sato and his colleagues, BA.4 and BA.5 may have evolved to favour infecting lung cells.
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This differs from earlier, milder Omicron variants, which separate data suggests did not grow as well in cells derived from lungs.
Mr Sato told ITV News: "We have data suggesting that BA.4/5 spike is more fusogenic [facilitates fusion] than BA.2 spike. In our previous studies on Delta, BA.1 and BA.2, higher fusogenicity is closely associated with lung preference."
Total Covid infections in the UK are now back at levels last seen at the start of May, but remain well below the record 4.9 million at the peak of the Omicron BA.2 wave at the end of March.
What are Covid levels like across the UK?
All four nations have seen an increase in cases.
In England, 1.1 million people were likely to test positive for Covid-19 the week on July 6 – the equivalent of around one in 50. This is up week-on-week from 797,500, or one in 70. Wales has seen infections rise to 64,800 people, or one in 45, up from 40,500, or one in 75. The virus is estimated to be most prevalent in Scotland, where 176,900 people were likely to have tested positive last week, or one in 30, up from 124,100, or one in 40. Northern Ireland has seen Covid-19 infections jump to an estimated 42,900 people, or one in 45, up from 27,700, or one in 65.