A brief look at the Omicron subvariant that’s currently making the rounds
It can feel like a revolving door when it comes to new SARS-CoV-2 variants and Omicron sublineages. The latest to emerge, XBB.1.16 – nicknamed “Arcturus” by scientists – is currently being tracked by the World Health Organization as a variant of interest, alongside its close relative, XBB.1.5.
In a report released on April 27, the WHO reported that XBB.1.5 accounted for 45.9 percent of sequences and was reported in 103 countries between April 3–9, 2023; in the same week, XBB.1.16 had been reported from 37 countries and made up 4.3 percent of sequences – a 1.3 percent increase from just four weeks earlier.
Shishi Luo, Head of Infectious Disease at viral surveillance and population genomics company Helix, California, US, tells me, “XBB.1.16 is a sublineage of XBB.1, which is a recombinant lineage of two BA sublineages. It has gained attention recently because i) it is dominant in India, ii) the WHO mentioned it as a variant it is monitoring, and iii) the CDC started reporting it in its variant tracker because its frequency in the US is above 1 percent.”
XBB.1.16 doesn’t appear to be more severe than its predecessors, but reports of a novel symptom have emerged. “There have been reports of association between XBB.1.16 infection and conjunctivitis,” says Luo. “Although conjunctivitis is generally associated with respiratory infection, it hasn’t been prominently associated with COVID-19 infection until now.”
As we inch closer to summer and away from respiratory disease season in the northern hemisphere, Luo says it’s unlikely that XBB.1.16 will trigger a new wave of COVID-19 cases. And although it has increased in frequency, Luo notes, “Each successive wave of Omicron sublineages has been more attenuated than the previous one.” When asked about immunity against XBB.1.16, Luo says it is too early to say anything definitive; however, she does share a working hypothesis: “The bivalent vaccine and prior infection will provide the same level of protection against XBB.1.16 as the currently dominant variant XBB.1.5.”
Why do Omicron sublineages keep emerging rather than new variants? “Since almost all the currently circulating SARS-CoV-2 lineages are descended from Omicron, we are much more likely to see an Omicron sublineage emerge than something entirely new,” Luo explains. “Incidentally, the WHO recently updated their working definitions of variants so that, in future, a sublineage of Omicron could receive a new Greek letter, but only if certain criteria are met.”