Albertans urged to protect themselves as highly transmissible XBB.1.5 subvariant shows signs of growth
Infectious disease experts are warning the more transmissible XBB.1.5 Omicron subvariant appears on the rise in Alberta and it should be taken seriously.
XBB.1.5, which evolved from two BA.2 sublineages, carries mutations that scientists say give it a growth advantage.
Last week the province confirmed four cases of the latest Omicron offshoot have been identified through genome sequencing — a process that can take several weeks.
More telling, experts say, is that wastewater tracking, which doesn't break down BA.2 signals by sublineages, shows the umbrella category of BA.2 variants is growing as a proportion of the total.
It's rising quite quickly in some areas of the province including Calgary and nearby communities.
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"We do see it in wastewater in most zones of the province," said Dr. Stephanie Smith, an infectious disease physician at the University of Alberta Hospital.
"We're certainly seeing some areas that have quite high proportions … in their wastewater. So I suspect there's way more than the confirmed number of cases than public health has stated."
According to Smith, the increasing BA.2 signal in wastewater is very likely driven by the XBB.1.5 strain and she expects it will account for at least half of Alberta's COVID-19 cases in the next four weeks.
Alberta Health statistics also show BA.2 variants have been growing as a proportion of PCR-confirmed cases for a number of weeks now. As of Jan.7, BA.2 accounted for seven per cent of cases.
"Based on the data that we're seeing out of the U.S. I suspect that [XBB.1.5] will fairly quickly eclipse BA.5 which is predominant in many areas right now."
The U.S. Centers for Disease Control estimated XBB.1.5 accounted for 27.6 per cent of COVID-19 cases in that country during the first week of January.
B.C.-based COVID modeller and epidemiologist, Caroline Colijn, is watching XBB.1.5 closely as well.
"It's rising in Canada right now, we think, at a rate of about nine or ten per cent a day compared to the other lineages that were predominant before, " said Colijn, a Canada 150 Research Chair at Simon Fraser University.
"It's around ten per cent [of cases] overall in Canada so it may be driving some rise in Alberta too."
According to Colijn, XBB.1.5 could spark another surge but it's difficult to predict how large any wave will be.
"It depends on how immune evasive and transmissible this strain is in our own community, in our own context. And it depends on what we do. So it depends on how much transmission there is, which depends on indoor activities and masking and all kinds of things."
Colijn said while this subvariant doesn't appear to cause more severe disease it is highly transmissible. And that can lead to a high number of infections.
"Even if it isn't more severe it could produce a much higher burden on our health systems and a much higher risk for individuals of getting severe disease."
Smith is also concerned about immune evasion, particularly given Alberta's low vaccine uptake.
"If people have had two doses of the original COVID vaccine and haven't been boosted with a bivalent vaccine they really don't have much immunity to this strain at all. And similarly if they've been infected with COVID, but greater than six months ago, then they're really not going to have much protection either," said Smith.
"That's really what makes me a little bit more nervous."
The evidence so far, she said, shows the bivalent vaccine works well against XBB.1.5.
"The initial data that we have does show that there's higher antibody responses and better protection against severe disease entirely," she said.
"Number one: please, please get vaccinated. Getting the booster — getting your bivalent vaccine — is going to provide you good protection. That's super important."
CBC News asked Alberta Health for an update on the number of confirmed XBB.1.5 cases this week, but that information was not provided.
"We are monitoring this new subvariant and managing cases as they emerge," spokesperson Charity Wallace said in an emailed statement, adding that XBB.1.5 cases will be included in BA.2 case reporting moving forward.
"We encourage Albertans to stay up-to-date on their immunizations … Wearing a mask, especially in crowded indoor settings, can help reduce the risk of becoming sick and help protect others from being exposed."
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