Omicron subvariant expected to become dominant strain in Ontario: science table head

The head of Ontario's COVID-19 science table says a subvariant of Omicron is soon expected to become the dominant strain in the province.

The growth rate of the BA.5 subvariant has outpaced all previous lineages of the virus, according to a recent report from Public Health Ontario (PHO).

Dr. Fahad Razak, scientific director of the province's COVID- 19 advisory table, said there is some cause for concern as BA.5 becomes the dominant strain.

Razak, an internist at Unity Health Toronto, said the variant is much better at getting around immunity, whether that immunity is from a vaccine, previous infection or both. He said immunity against the latest variant is "much weaker" when compared to previous Omicron subvariants like BA.1 and BA.2.

"It's not giving you a lot of protection against BA.5," Razak told CBC Radio's Metro Morning on Tuesday. 

"It's sufficiently mutated now, BA.5, that it has essentially presented your immune system with a different surface that it doesn't recognize and that's the challenge."

As of June 17, just over 18 per cent of people with two doses of COVID-19 vaccine who were hospitalized due to the virus had the BA.5 subvariant, according to PHO data.

In Ontario, providing a clear, full picture about the state of COVID-19 has become increasingly difficult over the last several months, after the government restricted lab testing and stopped publishing school-related data.

On June 11, the province also switched to weekly reporting of COVID-19 data after more than two years of daily updates. 

The latest wastewater data seen on the science table's dashboard, however, shows an uptick in the level of infection across the province. Razak said the rise in the level of infection seen over the last few weeks is significant, though "not as strong as before."

With the relaxing of most public health measures including the lifting of mask mandates earlier this month, Razak is urging Ontarians to continue wearing a mask in high-risk settings such as on public transit and in offices and malls.

"It's all about risk reduction, there's no black and white here anymore," he said. "It's about doing the individual steps you can to reduce risk where you can."

Razak said those who have their third and fourth vaccine doses still have "very strong protection" against severe illness. He noted, though, that health officials don't have enough information to know whether the BA.5 subvariant is more severe than others.

Bivalent vaccines, a new generation of vaccines currently in the making, will provide more protection against subvariants including BA.5, Razak said.