Arcturus COVID subvariant: What we know

Arcturus COVID subvariant: What we know

The COVID-19 subvariant, dubbed XBB.1.16 by the World Health Organization, was first detected in the Indian subcontinent in late January. It has since been detected in 29 countries, although experts say it is likely circulating undetected in many others. So far, XBB.1.16 does not appear to have been detected in Canada.

“We don’t know yet how this variant is going to pan out,” said Dr. Don Vinh, a professor in the departments of medicine, medical microbiology and human genetics at McGill University, in a phone interview with on Wednesday.

“There have certainly been variants that have emerged and then fizzled out, like the Gamma variant in South America, and there are clearly more often variants that have emerged and caused problems, like Omicron. I think what we have to do is be vigilante. “

The WHO hasn’t yet classified XBB.1.16 – informally nicknamed ‘Arcturus’ – a variant of concern or interest, referring to it instead as a “variant under observation.”

Here is what we know about the Omicron subvariant so far.


According to the World Health Organization’s April 13 epidemiological update, detections of the subvariant had been reported 2,222 times in 29 countries as of April 11.

XBB.1.16 is the recombinant – or a product of the mixing together – of the BA.2.10.1 and BA.2.75 subvariants. It is similar in profile to another variant, XBB.1.5, except that it has one additional spike protein mutation, which lab studies have shown could increase infectivity and disease severity.

However, the WHO said it has no evidence that the subvariant actually caused more severe illness than the previous variant. XBB.1.16 does appear to have a high growth rate, and it has driven a surge in cases and hospitalizations in India. So far, the WHO reports XBB.1.16 does not seem to have driven a rise in ICU admissions or deaths even in countries where case counts have driven up.

“Most of the sequences are from India, and in India XBB.1.16 has been replaced by other variants that are in circulation. So, this is one to watch. It has been in circulation for a few months,” said Maria Van Kerkhove, technical lead for COVID-19 response at the WHO, during a virtual media briefing on March 29.


Although XBB.1.16’s genetic makeup suggests it could lead to more severe COVID-19 symptoms, the data scientists have on the variant so far suggests it hasn’t been done so. People sick with SARS-CoV-2 and its variants – and subvariants – can experience a wide range of mild-to-severe symptoms.

These can include fever or chills, cough, shortness of breath or difficulty breathing, fatigue, muscle or body aches, headache, new loss of taste or smell, sore throat, congestion or runny nose, nausea, vomiting and diarrhea.

“It’s likely that it’s going to be more of the same in the sense that we might see a rise in cases and we might see a corresponding rise in hospitalizations associated with it,” said Dr. Isaac Bogoch, clinical investigator at the Toronto General Hospital Research Institute and associate professor at the University of Toronto, in a phone interview with on Wednesday.

“It’s extremely unlikely that it’s going to cause the same degree of pressure on our health-care system as we once saw earlier on in the pandemic.”


Neither Vinh nor Bogoch is aware of evidence that XBB.1.16 is circulating in Canada, however, both said that doesn’t mean it isn’t here or won’t be detected here eventually.

And although it hasn’t been shown to lead to severe symptoms in most people, Bogoch said even a variant that leads to mild illness can seriously impact provincial health-care systems, as Canada saw during the Omicron – or BA.1 – wave in late 2021 and early 2022.

“That initial wave was extremely challenging. It put considerable pressure on our health-care system because so many people were sick in such a short period of time,” Bogoch told in a phone interview on Wednesday.

“And even though hospitalizations weren’t all that common, there were so many people who were infected that a small percentage requiring hospitalization out of a large number of people who were infected ended up being a lot of people in hospital.”

Additionally, while many people infected with the subvariant might experience mild-to-moderate illness, seniors and people with immunocompromising conditions would face significant risk in the event of another variant-driven COVID-19 surge. Canada has reported 52,121 COVID-19 deaths since the pandemic began, many of which were in vulnerable, high-risk populations.

And Vinh pointed out that even mild cases of COVID-19 in otherwise healthy people can have lasting consequences.

“There are people who get infected, recover from it, but then develop the long-term complications of long COVID,” he said. “People think long COVID is that you can’t smell or your brain is foggy. But we also have…things like an increased risk of heart attacks or an increased risk of strokes in the months subsequent to that infection, even if they are mild in the acute phase.”

In short, Canadians shouldn’t dismiss XBB. 1.16 as a non-threat.

Fortunately, Bogoch said it’s highly likely the existing bivalent COVID-19 vaccine boosters provide some protection against XBB.1.16, just as they have with other Omicron subvariants. Other tried and tested precautions shown to reduce the risk of COVID-19 infection should also help protect against XBB. 1.16, should it begin circulating widely in Canada.

“No one wants to be infected with COVID or any other infection, so in the absence of large public health initiatives, people can take their own initiatives to reduce the risk of infection,” he said. “So that means putting on a mask in indoor settings, being up to date on vaccinations, which lowers the risk of more severe manifestations of the virus, things like that.”