Omicron variant BA.5 is gaining ground fast in Ontario. Here’s why experts are watching it closely

A new branch of COVID-19's Omicron variant, BA.5, is poised to become dominant in Ontario, and experts are watching closely, as it's much better at getting around immunity, whether that immunity is from a vaccine, prior infection or both.

That 50 per cent tip-over point is probably going to happen within this week, where it becomes the dominant lineage in Ontario, and it's clearly risen very quickly," says Dr. Fahad Razak, the scientific director of the Ontario COVID-19 Science Advisory Table.

If you trace back, you'll see that rise happened over the matter of a few weeks to about a month."

The proportion of BA.5, a sub-variant of Omicron, grew from 3.1 per cent to 6.7 per cent of sampled positive cases, from the last week of May to the first week of June, according to Public Health Ontario's most recent report tracking variants of concern.

The proportion of BA.5 was projected to reach about 44 per cent of samples this week.

Razak said he hasn't seen any serious signal to suggest" that BA.4 and BA.5 are sending more people to hospital compared to other Omicron waves, especially in countries with high levels of immunity. But the new cases are causing disruption."

I'm speaking to colleagues who are saying suddenly, three or four of their staff in the health-care system (are off sick) or someone who's running a business, suddenly people are getting sick again."

Since Omicron, a mutated and more contagious version of the original coronavirus, emerged in late 2021, the virus has continued to evolve.

BA.5 and another variation, BA.4, were first detected in South Africa earlier this year, and added to the WHO's list to track in April. They have also spread in Denmark, Portugal, the United States and the United Kingdom.

The main concern at this point, said Razak, is that there is emerging evidence," including two recent papers, from the New England Journal of Medicine and Nature, on BA.4 and BA.5's ability to get around immunity.

It looks like BA.4 (and) BA.5 are more evasive and have the potential to do two things," Razal said. They tend to have greater potential to infect someone who has been vaccinated, and they seem to have greater potential to reinfect someone, even if they've had an Omicron infection.

I think we have to watch carefully."

Omicron and its other sub-variants mutated enough from original COVID, so that people who were vaccinated could catch them, although they generally had protection from serious illness and death, especially with three shots.

Dawn Bowdish, the Canada Research Chair in aging and immunity and a professor of medicine at McMaster University, said that one of the main messages for the public is not to assume you're immune from getting the disease again, even if you've been recently infected.

If you got original Omicron in the winter, for example, that provides no more than three months' protection and sometimes not even that, even in people who are vaccinated," she said.

To further complicate the situation, it's now been six months since many Ontarians and Canadians got their third shot, so immunity from those shots is starting to fade, just as public health restrictions have been dropped.

She said our mentality needs to shift from an idea of being fully vaccinated," to one of keeping our shots up to date.

But many Ontarians are not yet eligible for a fourth shot. (Only those 60 and up, and a few other groups - such as those in long-term care, First Nation, Inuit and Metis adults and people who are immunocompromised - can currently get them.)

In Quebec, fourth shots are open to everyone 18 and up.

It is my professional opinion that we should start thinking about making sure we have as many people as up to date as possible," said Bowdish. It makes a lot of sense to get as many people vaccinated at the beginning of a wave as possible."

It seems there are no immediate plans to open up fourth doses more broadly in Ontario. In response to a question on this, Ministry of Health spokesperson W.D. Lighthall repeated the current eligibility criteria in an email.

Ontario is monitoring NACI's (the National Advisory Committee on Immunization) guidance in case of any additional recommendations on booster doses for additional populations," he added.

Razak said he's waiting to see how the scientific evidence develops, and for now both the Ontario and Quebec positions are reasonable."

There's also the hope of Omicron-specific vaccines on the horizon, that would be a better fit for the mutations the virus has undergone.

Moderna announced Wednesday that its Omicron booster (currently under development) generates antibodies against BA.4 and BA.5.

Canada's chief public health officer, Dr. Theresa Tam, said at a virtual news conference last week that officials are cautiously optimistic" about the state of the pandemic. But they are seeing growth in both BA.4 and BA.5 as well as BA.2.12.1 in Canada, which have demonstrated a growth advantage and additional immune escape over BA.1 and BA.2." (BA.1 dominated in Ontario in December and January, then was overtaken by BA.2 and BA.2.12.1.)

COVID-19 has shown us over the past few years that there may be more surprises ahead," she added. Viral evolution and waning immunity are anticipated to impact COVID-19 activity going forward."

Tam urged Canadians to stay up to date" with COVID vaccinations, as well as wear a well fitted mask, and stay home while sick.

Bowdish is hopeful that more holding their gatherings outdoors during the summer months and the fact that school is out soon may temper the spread of BA.5.

But she's also concerned about already overstretched and burned-out health-care staff if cases and hospitalizations rise again.

I'm so worried about what the next wave will bring," she said. It's not over."

May Warren is a Toronto-based breaking news reporter for the Star. Follow her on Twitter: @maywarren11