As temperatures drop and more Canadians head indoors, the familiar sniffles, aches and pains may soon follow, signaling the arrival of cold and flu season.

In Canada, flu season typically runs from November to April, and while anyone can catch the flu, the virus can sometimes lead to severe complications — even death, which is why experts stress the importance of the annual flu shot.

In preparation,  some provinces are rolling out this year’s influenza shot over the next few weeks, beginning with vulnerable groups before expanding to the general public.

The dominant strain this year is expected to be influenza H3N2, with some H1N1 and influenza B circulating as well, though not in excessive amounts, according to Gerald Evans, an infectious disease specialist at Queen’s University in Kingston, Ont.

“We have a fair bit of data from South America, Australia and New Zealand showing it’s an H3N2 year,” he said, adding that what happens in the Southern Hemisphere usually lays the groundwork for predicting which viruses are out there by the time they make their way north.

H3N2 is a form of influenza A and tends to cause more severe illness, particularly in older adults, young children and those with weakened immune systems.

It’s not just influenza that Canadians need to worry about — fall and winter also bring a rise in other respiratory illnesses, including rhinovirus (the common cold), respiratory syncytial virus (RSV), and COVID-19.

Here is a look at what may be in store for this season.

Based on trends from countries in the southern hemisphere, this year’s influenza season in Canada will overall be considered “average,” Evans said.

In countries like Australia, the flu season was not early, running as usual from May to September, with an increase in cases during June and July. This pattern may indicate that Canadians could experience a peak in flu cases in late December and January, Evans explained.

“So our expectation would be a very typical season, starting in late December and early January, but it can be as late as February in March. And sometimes we see second waves,” he said.

But the onset of influenza season can be unpredictable, as Evans noted that it is often influenced by travel patterns. If there is an increase in travel from the southern hemisphere, it could lead to an earlier introduction of the virus.

“And of course, that’s all important because we look at our flu shot annual campaign to get flu shots into people to reduce the severity of disease,” he added.

Kevin Chan, a pediatric emergency doctor based in London, Ont., said that respiratory illnesses like RSV, typically start around later October and early November, depending on the year, and can spike very quickly.

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“What the Australians saw was they had a typical respiratory system season with influenza A, B and COVID. But one of the interesting things that they saw in Australia was that if you got sick with one virus, you were actually more prone to gets getting sick with other viruses,” he warned.

While influenza caused some illnesses and deaths in the southern hemisphere, the rates remained relatively average for what is typically expected, Evans said. But these numbers were significantly overshadowed by the continuing effects of COVID-19, he added.

“COVID was still accounting for most of the more severe cases, hospitalizations and deaths, particularly in Australia,” he said.

Canadians can expect a few key trends regarding COVID-19 this flu season, he said. Although the summer wave of COVID-19 appears to have peaked, the decline is slow. And with colder weather forcing more people indoors, he said we should anticipate a rise in cases.

“But the availability of new vaccine formulations by the end of September could help mitigate the impact of COVID-19 during the winter months,” he said.

The best way to protect yourself from respiratory illnesses is by getting vaccinated, according to the Public Health Agency of Canada (PHAC). Vaccines are available for influenza, RSV and COVID-19, but their availability may vary depending on several factors such as age and location.

The flu shot is recommended for almost everyone who is six months of age and older, PHAC said. It protects against three or four different strains of the flu virus each season.

Receiving the annual vaccine helps protect you in several ways, PHAC stated.

It reduces the risk of severe illness from flu-related complications, safeguards those around you by lowering the likelihood of spreading the virus and decreases the overall burden on the health-care system during the respiratory virus season.

“When it comes to influenza, it really is the flu shot that’s going to help to keep you with a milder illness,” Evans said.

“Influenza is a pretty nasty infection when you get it. And what the flu shot does is it helps to make that a lot less severe, especially in very high-risk individuals. So those are very young and the very old, as well as some people who have underlying cardiac or respiratory diseases. It can be the difference between surviving an episode of flu in the hospital versus dying,” he added.

The flu and COVID-19 are caused by different viruses. This means that the flu vaccine won’t protect you against COVID-19, PHAC warned.

Starting in the fall of 2024, the National Advisory Committee on Immunization (NACI) strongly recommends the most recently updated COVID-19 vaccines for previously vaccinated and unvaccinated individuals at increased risk of COVID-19.

Two updated mRNA vaccines (both targeting the KP.2 strain) are authorized for fall 2024 for those six months of age and over. Moderna’s SpikeVAX is available for those six months of age and over, and Pfizer’s Comirnaty shot is available for those 12 years of age and over.

The availability date for the COVID-19 vaccine has not yet been announced.

When it comes to RSV protection, vaccines are now available for older adults and pregnant individuals. Depending on the province,  families with infants and high-risk children two years old or younger will be able to access a publicly funded RSV vaccine.

This fall and winter, Ontario, Quebec and Nunavut will offer the newer monoclonal antibody nirsevimab — approved by Health Canada in the spring of 2023 —  to all babies going through their first RSV season.

“I think if we can get in front of the peaking — that should start in late October and early November — if we can get the vaccines out by the beginning of October, I think we should prevent a big amount of the respiratory diseases from coming to our hospitals,” Chan said.

Aside from vaccines, Evans emphasized that the most fundamental way to protect yourself, especially during respiratory season, is regular hand washing.

“I always say it’s an easy thing to do, and certainly alcohol-based hand rubs work well,” he said. “Washing your hands is another important attribute to do to reduce your risk for infections.”