XBB1.5: Here’s what we know about the ‘most transmissible’ COVID strain yet

XBB.1.5, a new COVID-19 strain that has been spreading rapidly in the United States is now the “most transmissible subvariant that has been detected yet,” the World Health Organization says.

The subvariant of Omicron has been detected in 29 countries to date, the WHO said during a briefing Wednesday.

It is now responsible for approximately 70 per cent of new COVID-19 cases in the Northeastern U.S., which represents a massive growth rate since early December, when it accounted for just four per cent of new U.S. COVID cases, according to data from the U.S. Centers for Disease Control and Prevention (CDC).

“We are concerned about its growth advantage in particular in some countries in Europe and in the U.S., in North America, particularly the Northeast part of the United States, where XBB.1.5 has rapidly replaced other circulating variants,” said Dr. Maria Van Kerkhove, WHO’s technical lead for COVID-19, on Wednesday.

“Our concern is how transmissible it is, … and the more this virus circulates, the more opportunities it will have to change.”

The Public Health Agency of Canada (PHAC) told Global News it is aware of 21 detections of the XBB.1.5 variant in Canada as of Jan. 4, but added that proportions and growth rates will not be reported until there is sufficient data.

“As with all COVID-19 sub-lineages, PHAC continues to carefully monitor the spread of XBB,” the agency said in a statement to Global News.
“XBB.1.5 is currently considered to be only detected sporadically. As data rolls in, growth rates can be more accurately estimated.”

The agency did not identify whether it considers this mutation to be a variant of concern, noting a number of complex factors that play into such a decision, including whether scientists and public health officials observe an actual change in the behaviour of the virus.

“The government of Canada has a strong monitoring program in place with the provinces and territories to identify COVID-19 variants in Canada, including the Omicron variant of concern and its sublineages,” PHAC said in its statement.

But experts say, given the proximity of where the virus is spreading in the U.S., it’s only a matter of time before the virus is more prevalent in Canada.

“Let’s be frank, XBB.1.5 has predominated as the major variant that’s circulating in the Northeastern United States. That’s pretty much right at our door,” said Dr. Donald Vinh, a medical microbiologist at the McGill University Health Center in Montreal.

“Therefore, believe it or not, it probably crept already through our door and has probably done so within the last month, right under our noses, without us being able to adequately monitor, survey or report on it.”

Here’s what is known so far about XBB.1.5 and what infectious diseases experts are watching for when it comes to this new COVID-19 strain.

This new subvariant, which is a sublineage of the Omicron subvariant XBB, has already become a dominant strain in the United States, making up over 75 per cent of new COVID cases in New England, New York and New Jersey and now accounts for over 40 per cent of new COVID cases in America overall, according to the CDC.

The severity of illness that it causes is not yet known, WHO says, but this is being assessed by a technical advisory group to the UN agency with details to be released in the coming days.

Deaths from COVID-19 overall across the globe have gone up by 15 per cent in the last month, marking a reversal of a downward trend in pandemic mortality in the last several months, Van Kerkhove said Wednesday.

However, there’s still no indication this new variant is to blame, nor is there data to suggest severity of illness is worse with XBB.1.5, she added.

“That is something that we are watching very closely through experimental studies in the lab, but also in real world data, when we look at hospitalization rates around the world among people who are infected with this subvariant.”

Infectious diseases experts say existing COVID-19 vaccines, especially the newer bivalent boosters, remain an important tool to protect against severe illness – and when it comes to XBB.1.5, that message hasn’t changed.

“We know that the booster vaccines really still do a remarkable job in protecting people against more severe manifestations of the virus like hospitalization and death,” Dr. Isaac Bogoch, an infectious diseases specialist and associate professor at University of Toronto’s Temerty Faculty of Medicine, said Tuesday evening in an interview on A Little More Conversation with Ben O’Hara-Byrne, a Corus-owned radio program.

Remaining up-to-date with vaccination is especially important for older Canadians and those underlying risk factors for severe disease, he added.

WHO officials echoed these sentiments Wednesday, noting that social gatherings over the holidays mean health officials worldwide are expecting increased transmission of the virus.

Hospitalizations have increased in the U.S. in recent weeks, Van Kerkhove confirmed Wednesday, which is one of the indicators that WHO scientists will be delving into in their risk assessment of XBB.1.5.

But increased hospitalizations don’t have to mean increased deaths, Van Kerkhove said.

“Vaccination remains absolutely critical to preventing severe disease and death no matter where you live,” she said.

However, some preliminary data, including a December study published in the medical journal Cell, suggest XBB.1.5 may be able to evade previous immunity an individual may have acquired through vaccination and previous infection.

While all new variants and sublineages of COVID-19 over the last three years have shown new levels of immune evasiveness, early data on this new strain is concerning, Vinh said.

“The concern we’re seeing is that XBB and its lineages are what we call evasive because of the mutations that they carry – they have now the capacity to evade immunity that was acquired through older vaccinations and older infections, including some of the recent infections,” Vinh said.

“So that that tells us that if you have a vaccination status that is out of date, for example more than four to five months old, or only (have been vaccinated) with the monovalent vaccines and not the recent bivalent ones, or if you had a recent infection, say, around November or December, those characteristics may not be enough to protect you from getting infected with XBB.”

That’s why taking additional non-pharmaceutical protection measures such as masking, physical distancing and improving ventilation are also recommended, especially for those at high risk of severe outcomes from COVID-19, Bogoch said.

“We know that we can put a mask on in crowded indoor settings where we know the vast majority of the virus is transmitted and, you know, we can navigate through this just like we’ve navigated through the other waves.”

While experts say it’s only a matter of time before this new subvariant begins showing up across the country, they remain optimistic Canada can weather this new upcoming wave.

Previous waves of Omicron subvariants, including BA.1 and BA.5, did result in new infections, hospitalizations and deaths.

But those upticks in COVID cases weren’t nearly as significant and impactful on the health care system as the initial Omicron wave, he said.

“So the hope, of course, is that future waves of COVID will …  have less and less of an impact on our health-care system and our on our other sectors as we build up more community level protection through vaccination and through recovery from infection, with the caveat that, of course, we don’t want people to be infected.”

Dr. Sameer Elsayed, professor of medicine, epidemiology and biostatistics at Western University, agreed.

“In terms of worry, I think we just have to just try our best,” he said.

“If we’re sick, we stay at home, we can mask, and we should mask. And if we can stay away from other people at work, we should continue to employ social distancing measures.”