Arcturus: the new Covid variant surging in India

A new Covid subvariant that is feared to be the most infectious yet has triggered a surge of infections in India.

Covid cases across the vast South Asian country have increased 13-fold in the past month, with the Health Ministry recording a total of 40,215 active cases yesterday following a single-day rise of 7,830 new infections.

As hospitals nationwide are put “on red alert”, said the i news site’s science correspondent Tom Bawden, the outbreak “wreaking havoc” in India is being blamed on Arcturus, a variant that has also been reported in dozens of other countries including the UK.

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What is Arcturus?

Arcturus, or XBB.1.16, is an Omicron subvariant that was first detected in late January and and has since been monitored by the World Health Organization (WHO) as a variant of concern.

Arcturus has spread rapidly across India, where face masks are once again compulsory in some states, for the first time in more than a year, and officials are demanding that testing be ramped up.

It has also been identified in at least 26 other countries.

In the UK, another Omicron variant, Kraken (XBB.1.5), was the dominant strain as of the end of February, accounting for just over half of cases, latest ONS data shows. Arcturus currently accounts for less than 1% of UK cases, according to the GISAID database (Global Initiative on Sharing All Influenza Data), the biggest tracker of Sars-CoV-2 sequences.

“But that share is expected to increase considerably,” said the i news site’s Bawden.

The new variant has not been found to be more severe than other strains. However, it has an additional mutation which “in lab studies shows increased infectivity as well as potential increased pathogenicity”, Dr Maria Van Kerkhove, the WHO’s technical lead for Covid, told a press conference at the end of March.

Arcturus currently accounts for about 5% of cases in the US and Australia, and 12% in Singapore, according to GISAID.

How is it different to other Covid subvariants?

Arcturus is nearly 1.2 times as transmissible as Kraken (XBB.1.5), until now the most infectious subvariant, according to a study by scientists from the University of Tokyo.

This higher reproductive, or “R”, number – a measure of how people many an infected person will go on to infect – suggests the subvariant “will spread worldwide in the near future”, the study authors wrote. The mutations in Arcturus “may contribute to increased viral growth efficiency”, they added, or be more difficult for the immune system to repel.

Omicron and its subvariants have been particularly good at evading immunity or antibodies, built up by prior infection or vaccination. The ability of Arcturus to “exhibit profound immune evasion” is comparable, the study said.

But Omicron-targeted booster shots “will provide some protection”, said Professor Lawrence Young, a virologist at the University of Warwick. “And the anti-viral drug paxlovid will continue to work as an effective treatment.”

However, the rise of Arcturus in India is a sign that “we’re not yet out of the woods”, Young told The Independent. “We have to keep an eye on it.” The situation highlights “the importance of genomic surveillance”, he continued, but “a lot of countries including our own have let our guards down a bit and we can’t be sure what variants are around and what level of infection they’re causing until we see a significant outbreak”.

In a stark warning, Young told the i news site that “with reduced levels of surveillance in the UK, waning immunity from previous infections and vaccinations, and the general level of complacency, we are not well-equipped to handle another wave of infection”.