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New Covid strain raging through India more infectious than others

A new Covid variant called Arcturus, which is wreaking havoc in India – with more than 3 000 cases reported daily – has already touched down in a number of countries, including Britain, where about 50 cases have been detected.

Hospitals in India are on red alert, with compulsory face masks being brought back in some states to curb exploding infection rates that have soared 13-fold in the past month.

Arcturus (scientific name XBB.1.16) is a spin-off of Omicron, and thought to be the most contagious variant yet, reports Daily Mail, with the UK Health and Security Agency saying data collected from variant trackers reported that Britain has now sequenced almost 50 samples of Arcturus.

Officials in India believe the variant is single-handedly driving the latest wave.

The nation’s Ministry of Health ran mock drills last week to check how prepared its hospitals were for another potential influx of patients. And some states have brought back face masks in public settings, the first time for more than a year in some areas.

The drills and return of masks are a grim reminder of how the country was devastated by the Delta wave in 2021, with a total of 4.7m excess deaths, according to WHO estimates.

India’s Ministry of Health said there were 40 215 active Covid cases on 12 April, up by 3 122 in just one day.

These cases can include those who test positive while unwell at home as well as those in hospital.

Separate figures from the Oxford University-run platform Our World in Data show new daily cases hit 3 108 on 4 April, up from 242 one month earlier.

The variant has now been detected in 22 countries, with The Independent saying experts believe that its spike protein mutations could make it more aggressive. It causes novel symptoms in children, including conjunctivitis.

Virologist Professor Lawrence Young from the University of Warwick said the rise of the new variant in India was a sign that “we’re not yet out of the woods”.

“We have to keep an eye on it,” he said. “When a new variant arises you have to find out if it’s more infectious, more disease-causing, and is it more pathogenic?

“These kinds of things highlight the importance of genomic surveillance, but a lot of countries, including our own, have let down our guard 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.”

Data analysed by The Independent showed that many countries have significantly scaled back their testing, vaccination and tracing capabilities, meaning that many would be unprepared if the world were to be hit by another deadly Covid strain.

If a new deadly variant of Covid were to hit, high levels of testing would allow countries to make more targeted healthcare interventions, as opposed to implementing another costly, large-scale lockdown.

The latest testing data, as tracked by analysts at Our World in Data project, show that testing levels have plummeted.

In Europe, testing fell from 613 daily tests per 1 000 people at the start of 2022 to negligible levels by July of the same year.


Vaccination has been another key tool in the fight against the coronavirus, giving recipients high levels of immunity even as deadly earlier strains raged in 2021. More than 5bn people worldwide have now received a Covid jab.

However, vaccines do not remain 100% effective for ever. One 2021 study reported by the US Centres for Disease Control and Prevention (CDC) showed that vaccine effectiveness against infection dropped from 91.8% to 75% in the state of New York over the space of just a few months.

Many countries, including the UK, have now stopped widespread vaccinations, and have instead offered booster shots to more targeted groups, such as older people and those who are immunocompromised.

Globally, daily vaccination rates have fallen by a massive 99% since summer 2021 to around 250 000 doses per day. Across the world, thousands of vaccine centres have shut, and vaccine manufacturing has also plummeted. It would take some time to turn these trends around.

Around 30% of the world’s population – largely in the global South – remains unvaccinated against the disease, while the majority of countries also no longer trace the contacts of those who are infected with Covid, meaning they are unable to effectively follow and monitor the spread of any new outbreak.

The WHO said it is monitoring the strain, first detected in late January.

Dr Maria van Kerkhove, the WHO’s Covid technical lead, said: “It’s been in circulation for a few months. It has one additional mutation in the spike protein which in lab studies shows increased infectivity as well as potential increased pathogenicity.”

She added that while XBB.1.16 had been detected in other countries, most sequences were from India, where it had replaced other variants.

Meanwhile, a study by Japanese scientists has suggested Arcturus is 1.2 times more infectious than the closely-related Kraken Covid strain.

Uploading their findings to the biology research website bioRxiv, they wrote that this advantage suggests the new variant will “spread worldwide in the near future”.

They attributed this to mutations that could make it more difficult for the immune system to tackle and increase its growth rate. They added, however, said there is no evidence that Arcturus had any greater ability to evade the protection offered by vaccines or prior infection, compared with Kraken.

Kraken was the dominant strain in the UK by the end of February, causing 50.4% of cases.

As with other Covid variants, virus trackers online followed a pattern of naming new strains after mythological entities, and decided to call XBB.1.16 Arcturus,

Arcturus means Guardian of the Bear, and is related to the constellation called the Great Bear.

Study details

Virological characteristics of the SARS-CoV-2 Omicron XBB.1.16 variant

Daichi Yamasoba, Keiya Uriu, Arnon Plianchaisuk, Yusuke Kosugi, Lin Pan, Jiri Zahradnik, The Genotype to Phenotype Japan (G2P-Japan) Consortium, Jumpei Ito, Kei Sato.

Posted on bioRXiv on 9 April 2023


At the end of March 2023, XBB.1.16, a SARS-CoV-2 omicron XBB subvariant, emerged and was detected in various countries. Compared to XBB.1.5, XBB.1.16 has two substitutions in the S protein: E180V is in the N-terminal domain, and T478R in the receptor-binding domain (RBD). We first show that XBB.1.16 had an effective reproductive number (Re) that was 1.27- and 1.17-fold higher than the parental XBB.1 and XBB.1.5, respectively, suggesting that XBB.1.16 will spread worldwide in the near future. In fact, the WHO classified XBB.1.16 as a variant under monitoring on March 30, 2023. Neutralisation assays demonstrated the robust resistance of XBB.1.16 to breakthrough infection sera of BA.2 (18-fold versus B.1.1) and BA.5 (37-fold versus B.1.1). We then used six clinically-available monoclonal antibodies and showed that only sotrovimab exhibits antiviral activity against XBB subvariants, including XBB.1.16. Our results suggest that, similar to XBB.1 and XBB.1.5, XBB.1.16 is robustly resistant to a variety of anti-SARS-CoV-2 antibodies. Our multiscale investigations suggest that XBB.1.16 that XBB.1.16 has a greater growth advantage in the human population compared to XBB.1 and XBB.1.5, while the ability of XBB.1.16 to exhibit profound immune evasion is comparable to XBB.1 and XBB.1.5. The increased fitness of XBB.1.16 may be due to (1) different antigenicity than XBB.1.5; and/or (2) the mutations in the non-S viral protein(s) that may contribute to increased viral growth efficiency.


bioRXiv article – Virological characteristics of the SARS-CoV-2 Omicron XBB.1.16 variant (Open access)


Daily Mail article – Arcturus is already in the UK: Warning over new Covid variant causing carnage in India – and it may have been in Britain for a month (Open access)


The Independent article – Why the world is unprepared if new Covid variant Arcturus proves deadly (Open access)


See more from MedicalBrief archives:


Pandemic far from over as kraken sub-variant and surge in China show


COVID cases soar in China, ‘impossible’ to track


Surge of 300 COVID variants with increased immune escape properties


COVID-19 might have killed four million people in India – Harvard study





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