New Omicron subvariant expected to become dominant COVID-19 strain in Ontario

A new subvariant of Omicron is expected to become the dominant strain of COVID-19 in Ontario, health officials say.

According to the latest epidemiology summary by Public Health Ontario (PHO), the BA.5 subvariant has “the fastest comparative growth rate of any lineage in Ontario.”

The proportion of BA.5 in sampled positive cases grew from 3.1 per cent to 6.7 per cent between the last week of May and the first week of June, officials found. The weekly growth rate is also 3.22 times that of the BA.2 subvariant over the past 12 weeks.

“Based on that European data, and other data as well as that, it seems to be more transmissible than the BA.2 variant,” Dr. Samir Patel, chief of microbiology and laboratory science with PHO, told CTV News Toronto on Monday.

By the end of the month, Patel is projecting that just over 50 per cent of all COVID-19 cases in the province will be the BA.5 subvariant.

“This is consistent with what we're seeing internationally as well,” he added.

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The BA.5 subvariant of Omicron has been fueling a rise in cases in the United States as well as multiple European countries. Last week Chief Public Health Officer of Canada Dr. Theresa Tam noted that BA.5 made up about 6.5 per cent of COVID-19 cases in Canada.

Patel says that health officials don’t have enough information to say whether the BA.5 subvariant is more severe than the others, but they are “keeping an eye on it.”

“It is more transmissible so we are seeing BA.5 infection in individuals who have had their full dose of vaccination … but we're also not seeing severe disease as well,” Patel said. “We do need more data to be able to conclusively say that, yes, you know, people who are vaccinated, they may get infected, but the hospitalization rate or the severity is going to be low.”

Patel added that officials still recommend getting vaccinated against the novel coronavirus as it will likely provide some protection against hospitalization, regardless of the subvariant. This was echoed in new data provided by researchers at Beth Israel Deaconess Medical Center, who found that the new subvariants are more likely to evade antibodies.

"These data show that the BA.2.12.1, BA.4, and BA.5 subvariants substantially escape neutralizing antibodies induced by both vaccination and infection,” the researchers wrote in the New England Journal of Medicine.

According to PHO data as of June 17, just over 18 per cent of patients hospitalized with at least two doses of COVID-19 vaccine were related to the BA.5 subvariant. Patel argues that this statistic is not concerning as the more a variant spreads, the more likely it is to naturally infect a higher number of people, regardless of vaccination status.

"We need to all get vaccinated," he said. "If you're eligible for the third booster, you should get vaccinated... (if) you're eligible for fourth booster you should get vaccinated as well."

It’s yet unclear how the emergence of a new dominant strain will impact the overall COVID-19 case count in Ontario or the province’s health-care system, but according to data provided by the Science Advisory Table, it appears as though the concentration of novel coronavirus in wastewater is starting to slowly increase.

Most regions, with the exception of public health units in the southwest, are seeing an upwards tick in COVID-19 concentration in wastewater signals.

Just one month ago, public health officials noted an increase in BA.2.20 subvariants in Ontario.