COVID and flu season will soon collide. How bad will it be?

In a few months, the COVID pandemic is going to collide with Canada's unofficial fifth season - flu season.

What happens then is anyone's guess but experts are cautiously hopeful the impact might not be as severe as originally feared.

To predict the severity of our flu season, look south of the equator - Australia, typically - which is just wrapping up winter.

Australia had almost no flu season this year in large part because their flu season coincided with the major first wave of the COVID-19 pandemic," said Matthew Miller, a McMaster University infectious diseases specialist.

They did a good job of explaining to the population how bad it could be if we saw high rates of influenza and COVID-19 at the same time," Miller said.

Australia saw record levels of flu vaccinations this year, which helped, Miller said, but it appears behavioural changes related to COVID - restrictions on gatherings, physical distancing, mask wearing and hand hygiene - were just as important in keeping the flu at bay.

Given that we're still employing some of these restrictions, there's hope it will translate into fewer flu cases here.

In Canada, as long as people continue to respect as much as possible government guidance around physical distancing and masking, I think we might hope to have a more blunted flu season," said Miller.

However, there's one caveat, said Dr. Zain Chagla, the co-medical director of infection control for St. Joseph's Healthcare Hamilton.

Winter in Australia and winter in Canada are still very different." said Chagla.

Unlike a Canadian winter with -10 C to -20 C temperatures, Chagla said, the winter temperature in Melbourne is still in the 10 to 15 degree range, where the outdoors is still a usable setting."

Despite that, Chagla is optimistic. Typically, the flu season in Canada is declared over around mid-May but this year, health authorities stopped tracking cases in early April because flu rates were at historically low levels.

What will make this year more challenging, Chagla said, is that the symptoms for COVID and the flu are very similar.

Peeling them apart, particularly in people who are presenting to health care with symptoms of one or the other, is going to be very difficult," Chagla said. It's going to trigger a lot more testing and a lot more isolation."

Another challenge is that more parts of the economy have opened up, more people are back at work, and children will soon be heading back to school. Children are considered the primary drivers of influenza transmission.

Local hospitals haven't been overwhelmed with COVID cases but they're still running close to capacity, Chagla said.

There still is a worry that we're going to be over capacity to a significant amount and the solution isn't going to be putting people in hallways because that's not safe from an infection control standpoint," Chagla said

Convincing large numbers of people to get a flu vaccination will be critical this year, he added.

Typically, the flu vaccination rate in Canada is about 40 per cent of the population. Even among health-care workers, it's only 50 to 60 per cent.

This is probably going to be the last major mass vaccination campaign prior to getting a COVID-19 vaccine," Chagla said.

If we can't get an influenza vaccine campaign to hit high numbers, like 80 to 100 per cent, how the heck are we going to get a COVID-19 vaccination campaign to hit 80 to 100 per cent?"

Steve Buist is a Hamilton-based investigative reporter at The Spectator. Reach him via email: sbuist@thespec.com

Why is influenza prevalent in winter and early spring?

1. The influenza virus is less stable when the air is hot and humid, said Matthew Miller, a McMaster University infectious diseases specialist.

2. In colder weather, people congregate together more frequently in close proximity, with greater chance to spread the virus.

3. Forced-air heating, and drier air also play a role. The mucosal membranes that line the mouth and nasal passages dry out and that allows the virus to get a better foothold and infect the respiratory system.

What strains of influenza circulate and how virulent will they be?

It's too early to know the severity of the coming flu season.

Typically, two strains of influenza A virus circulate - the H1N1 strain and the H3N2 strain.

One or the other usually dominates each season," Miller said.

The H3N2 strain tends to cause more severe symptoms, he added.

Australia recorded very few flu-related deaths and major outbreaks this winter, which makes experts hopeful this year's flu season won't be severe.

Can people be infected with both the flu and the coronavirus in the same season?

Yes. And the consequences could be serious.

If you hammer your lungs again with another severe respiratory infection, there's a serious possibility that your lung function could be substantially compromised because it's still in the process of recovering from something else," said Miller.