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What is XBB Covid? The new Omicron variant that has led to surge in cases

New Covid variants are sparking fresh health concerns as Omicron relatives XBB and XBB.1.5 have seen a surge in cases in countries worldwide.

It comes as UK-based health experts have suggested that up to 9,000 people are dying from Covid a day in China, where infections have dramatically risen following the country’s end to strict isolation rules.

The surge has prompted the UK and US governments to require all passengers arriving in the respective countries from China from 5 January to return a negative Covid result before travelling.

So what are the XBB subvariants and where have they been seen? Here is all you need to know:

XBB is a subvariant of the Omicron BA.2 variant, and XBB.1.5 is a subvariant of XBB.

It emerged as a “recombinant lineage between the second generation Omicron variants”, Professor Kei Sato wrote in a study by University of Tokyo, Hokkaido University and Kyoto University, posted to preprint server bioRxiv.

The Japanese researchers studied XBB’s characteristics in hamsters including transmissibility and immune resistance.

Their results suggested that the subvariant is highly transmissible and has developed resistance to immunity.

New Omicron subvariants XBB and XBB.1.5 are on the rise (REUTERS)
New Omicron subvariants XBB and XBB.1.5 are on the rise (REUTERS)

In October 2022, the World Health Organisation (WHO) also said there was early evidence to suggest that XBB has a higher reinfection risk, compared to other circulating Omicron subvariants.

However, in a fact-checking article conducted by Reuters in November, its team concluded that there was no evidence that XBB “is more deadly or causes more severe COVID-19 than the Delta variant”.

Where have cases of XBB been reported?

The Omicron subvariants have taken the US by storm as together they accounted for 44.1per cent of the total cases in the country for the week ending December 31.

The subvariants were previously reported as just XBB before this week.

Covid cases have seen a surge worldwide with Omicron subvariants rife in parts of the US (PA)
Covid cases have seen a surge worldwide with Omicron subvariants rife in parts of the US (PA)
China is seeing around 9,000 deaths a day after the country ended its strict isolation rules (AP)
China is seeing around 9,000 deaths a day after the country ended its strict isolation rules (AP)

Though the subvariants are currently dominant in the Northeast, they account for fewer than 10 per cent of infections in many other parts of the country, according to the U.S. Centers for Disease Control and Prevention on Friday (CDC).

XBB.1.5 has been detected in at least 74 countries and 43 US states, according to outbreak.info which uses data from the Global Initiative on Sharing Avian Influenza Data (GISAID).

These countries include the UK, China, India, Pakistan, Indonesia and Australia.