A new sublineage of the SARS-CoV-2 Delta variant is under strict watch by officials in the UK as a rising number of cases are proving to carry some new mutations that may increase transmissibility and survival in a host. The new variant, dubbed "Delta+" but scientifically designated as AY.4.2, now accounts for 6 percent of all COVID-19 cases in the UK as of a Public Health England report from October 1.
While the mutations may give it distinct advantages, experts suggest the current COVID vaccines will likely still protect against it. As a result, it is not yet classified as a Variant of Concern or Interest, but it remains closely monitored and some expect it to rise to the rank of variant under investigation soon.
AY.4.2 is an offshoot of the dominant strain in the UK right now, AY.4, more commonly known as Delta. There is limited information about it currently, bar the increasing percentage of sequenced COVID-19 cases reporting as AY.4.2. It has two significant mutations in the spike protein, which allows the virus entry into human cells, called Y145H and A222V. While they do affect the spike protein, they do not affect the receptor-binding domain (the region that binds to cells) and are not found on any other Variants of Concern, indicating they may have limited impact on how successful or transmissible AY.4.2 is over other Delta variants.
Professor Francois Balloux, director of University College London's Genetics Institute, explained the situation on Twitter and indicated that while AY.4.2 does have an approximate 10 percent increase in transmissibility, it does not account for the rising number of COVID-19 cases in the UK.
With limited cases of AY.4.2 cropping up in other countries, it remains a largely UK-based variant and will continually be monitored for any changes in prevalence.