Covid Variant 'Arcturus', Driving Recent Surges, May Show A New Symptom 'Not Seen In Earlier Waves': Paediatrician

Arcturus is a name popularised for XBB.1.16 by an Indian paeditrician, who said that the Omicron subvariant may be causing a new symptom that was not seen in earlier waves.

Arcturus, the name coined for the XBB.1.16 Omicron subvariant by a variant tracker, is driving the recent surge in Covid-19 cases in India. XBB.1.16 is the most transmissible Covid-19 variant yet, and is a recombinant of BA.2.10.1 and BA.2.75 sublineages, according to the World Health Organization (WHO). 

Arcturus is a term popularised by Vipin M Vashishtha, a paediatrician and former convenor of the Indian Academy of Paediatrics (IAP), who used Arcturus as a hashtag in a March 17 tweet. In the tweet, he wrote that the Arcturus variant has now been detected in at least 12 countries, with the highest cases being reported in India, followed by the United States, Brunei, Singapore and the United Kingdom. 

What new symptom is XBB.1.16 causing?

In a recent tweet, Vashishtha hinted at the fact that a new symptom may be associated with the Arcturus variant, which was 'not seen in earlier waves'. He wrote that he was getting paediatric Covid-19 cases after a gap of six months, and that the infants he treated were showing a new symptom: non-purulent, itchy conjunctivitis with sticky eyes. 'Non-purulent' means that the eyes did not contain pus. 

He said that an "infantile phenotype" appears to be emerging, which means that the XBB.1.16 variant may be associated with a new trait observed in infants. 

In earlier tweets, Vashishtha wrote that XBB.1.16 has a 140 per cent growth advantage over XBB.1.5, the variant which accounted for almost half of all the globally sequenced cases in early March.

Vashishtha also wrote that XBB.1.16 could succeed to wade through the herd immunity of Indians that successfully resisted variants such as BA.2.75, BA.5 and XBB.1.5, among others. 

According to Fortune Magazine, Maria Van Kerkhove, Covid-19 technical lead for the WHO, said that in the East, XBB.1.16 is considered to be the "one to watch". 

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All about the characteristics of XBB.1.16 or Arcturus

According to a preprint published April 9 in bioRxiv, the preprint server for biology, XBB.1.16 has two substitutions in the spike protein, compared to XBB.1.15. One of the substitutions was observed in the N-terminal domain, mutation in which is linked with a reduction in the effectivity of neutralising antibodies in vaccinated individuals, and the other substitution was observed in the receptor-binding domain, which binds to the ACE2 receptor on the surface of host cells. 

According to the new study, the reproductive number of XBB.1.16 was found to be 1.27- and 1.17-fold higher than XBB.1 and XBB.1.5 respectively. 

The average number of secondary cases per infectious case in a population made up of both susceptible and non-susceptible cases is known as effective reproductive number, according to the UK Faculty of Public Health. 

This suggests that XBB.1.16 will spread worldwide in the near future, the study authors noted. 

On March 30, 2023, the WHO classified XBB.1.16 as a "variant under monitoring", the study said. 

The study found that only sotrovimab, a monoclonal antibody with activity against SARS-CoV-2, exhibits antiviral activity against XBB variants, including XBB.1.16. 

The authors noted that similar to XBB.1 and XBB.1.5, XBB.1.16 is "robustly resistant" to a variety of anti-SARS-CoV-2 antibodies. 

According to the study, XBB.1.16 has a greater growth advantage in the human population compared to XBB.1 and XBB.1.5. 

The immune invasion of XBB.1.16 is comparable to that of XBB.1 and XBB.1.5. 

The authors concluded that mutations in the viral proteins apart from the spike protein may contribute to the increased viral growth efficiency of XBB.1.16.