Another new Covid variant is spreading – Here’s what we know about Omicron Ba.4.6


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BA.4.6 is a descendant of Omicron’s BA.4 variant. BA.4 was first detected in January 2022 in South Africa and has since spread worldwide alongside the BA.5 variant. Here’s everything you need to know about it.

BA.4.6, a sub-variant of the Omicron COVID variant that quickly gained traction in the US, is now confirmed to be spreading to the UK. The latest COVID Variant Brief from the UK Health Security Agency (UKHSA) noted that in the week starting August 14, BA.4.6 accounted for 3.3% of samples in the UK .

It has since grown to represent around 9% of sequenced cases. Likewise, according to the Centers for Disease Control and Prevention, BA.4.6 now accounts for more than 9% of recent cases in the United States. The variant has also been identified in several other countries around the world.

So what do we know about BA.4.6, and should we be worried? Let’s take a look at the information we have so far.

BA.4.6 is a descendant of Omicron’s BA.4 variant. BA.4 was first detected in January 2022 in South Africa and has since spread worldwide alongside the BA.5 variant.

How did it appear?

How BA.4.6 emerged is not entirely clear, but it is possible that it was a recombinant variant. Recombination occurs when two different variants of SARS-CoV-2 (the virus that causes COVID-19) infect the same person, at the same time. While BA.4.6 will be similar to BA.4 in many ways, it carries a mutation of the spike protein, a protein on the surface of the virus that 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 evade antibodies acquired during vaccination and previous infection.

Severity, infectivity and immune evasion Fortunately, Omicron infections generally cause less severe illness, and we have seen fewer deaths with Omicron than with previous variants. We would expect this to apply to BA.4.6 as well. Indeed, there have not yet been any reports that this variant causes more severe symptoms.

Is it more transferable?

But we also know that subvariants of Omicron tend to be more transmissible than previous variants. 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 Although this information is based on a preprint (a study that has not yet been peer-reviewed), other emerging data confirms it.

According to the UKHSA briefing, early estimates suggest BA.4.6 has a relative advantage of 6.55% over BA.5 in England. This indicates that BA.4.6 replicates faster 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 lower than that of BA.5 compared to BA.2, which was 45% to 55%.

Are COVID vaccines less effective against the new variant?

The University of Oxford reported that people who received three doses of Pfizer’s original COVID vaccine produced fewer antibodies in response to BA.4.6 than to BA.4 or BA.5. This is concerning as it suggests COVID vaccines may be less effective against BA.4.6.

The ability of BA.4.6 to evade immunity can, however, be addressed to some extent by the new bivalent boosters, which specifically target Omicron, alongside the original strain of SARS-CoV-2. Time will tell us.

Meanwhile, a pre-print study shows that BA.4.6 escapes protection from Evusheld, an antibody therapy designed to protect people who are immunocompromised and don’t respond as well to COVID vaccines.

Vaccination is the key. The emergence of BA.4.6 and other new variants is concerning. This shows that the virus is still very much around and is mutating to find new ways to overcome our immune response to vaccination and previous infections. We know that people who have had COVID before can get the virus again, and this has been especially true for Omicron. In some cases, later episodes may be worse.

But vaccination continues to offer good protection against serious diseases and remains the best weapon we have to fight COVID. The recent approval of bivalent boosters is good news. Beyond that, the development of multivalent coronavirus vaccines that target multiple variants could provide even longer-lasting protection.

A recent study showed that a multivalent coronavirus vaccine administered through the nose elicited a strong immune response against the original strain of SARS-CoV-2, as well as two variants of concern, in mouse models.

Close monitoring of new variants, including BA.4.6, is urgent, as they could lead to the next wave of the COVID pandemic. For the public, it will pay to remain cautious and comply with all public health measures in place to prevent the spread of what remains a highly contagious virus.

(The author is a senior lecturer in medical microbiology at the University of Westminster in London)


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