At a time when the Covid-19 cases seem to be on the wane all across the world, BA.4.6, a subvariant of the omicron Covid variant is rearing its head with a few cases  reported from the US while confirmed to be spreading in the UK. It is not entirely clear how BA.4.6 has emerged, but it's possible, say experts, it could be a recombinant variant.

Recombination happens when two different variants of SARS-CoV-2 (the virus that causes COVID-19) infect the same person, at the same time.

The variant has also been identified in several other countries around the world. However, India is yet to report any such mutation, officials say here.  The latest briefing document on COVID variants from the UK Health Security Agency (UKHSA) noted that during the week beginning August 14, BA.4.6 accounted for 3.3per cent  of samples in the UK. It has since grown to make up around 9per cent of sequenced cases.

Similarly, according to the Centers for Disease Control and Prevention, BA.4.6 now accounts for more than 9per cent  of recent cases across the US. BA.4.6 is a descendant of the BA.4 variant of omicron. BA.4 was first detected in January 2022 in South Africa and has since spread around the world alongside the BA.5 variant.

While BA.4.6 will be similar to BA.4 in many ways, it carries a mutation to the spike protein, a protein on the surface of the virus which allows it to enter our cells. 

This mutation, R346T, has been seen in other variants and is associated with immune evasion, meaning it helps the virus to escape antibodies acquired from vaccination and prior infection.

Fortunately, omicron infections generally cause less serious illness, and we've seen fewer deaths with omicron than with earlier variants. We would expect this to apply to BA.4.6 too. Indeed, there have been no reports yet that this variant is causing more severe symptoms.

BA.4.6 appears to be even better at evading the immune system than BA.5, the currently dominant variant. Although this information is based on a preprint (a study that is yet to be peer-reviewed), other emerging data supports this.

According to the UKHSA's briefing, early estimates suggest BA.4.6 has a 6.55per cent  relative fitness advantage over BA.5 in England. This indicates that BA.4.6 replicates more quickly in the early stages of infection and has a higher growth rate than BA.5. The relative fitness advantage of BA.4.6 is considerably smaller than that of BA.5 over BA.2, which was 45per cent  to 55per cent .

The University of Oxford has reported that people who had received three doses of Pfizer's original Covid vaccine produce fewer antibodies in response to BA.4.6 than to BA.4 or BA.5. This is worrying because it suggests that Covid vaccines might be less effective against BA.4.6.