Influenza vs. RSV: What to know this sick season

An Alberta Health Services sign can be seen in this undated file photo. (File)

That severe respiratory syncytial virus (RSV) cases are outpacing influenza cases in Alberta this season is perhaps because several years of high influenza rates have paved the way for it to do so, a local infectious disease specialist says.

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According to the most recent government data, up to Jan. 11, the number of cases of each were only separated by a few hundred and the number of influenza deaths was still higher.

However, there were almost 500 more hospitalizations and nearly double the intensive care unit (ICU) admissions due to RSV.

This is a trend that has developed since the COVID-19 pandemic, says Dr. Lynora Saxinger at the University of Alberta Hospital.

“This year, RSV has been playing a relatively higher role because influenza has kind of receded more towards normal-bad level levels instead of extremely bad levels,” she told CTV News Edmonton on Friday.

She also says increased testing – the only definite way to diagnose RSV over influenza or even a cold, all of which have overlapping symptoms – may be a factor, but believes the larger contributor is the community’s resilience after two years of high influenza rates.

“On a population basis, we had less kind of partial built up immunity because of the gaps during the pandemic and we did see some switching of the dominant types of influenza over those two years, so it was basically just a more vulnerable population,” Saxinger explained.

“We’re kind of leading into more partial immunity from prior years epidemics, making it seem less severe now.”

This may also explain why influenza hospitalizations aren’t higher, given that only 20 per cent of Alberta’s population is vaccinated, the lowest coverage since the 2010-11 season, Saxinger said.

“People who have had influenza in the past two years are a little less likely to have influenza this year. And so people who’ve tended not to get influenza vaccination, many of them might have been infected in the last couple of more severe years.”

So far this season, the age group most likely to be hospitalized with influenza is 70-79 and admitted to the ICU is 60-69. Meanwhile, the majority – 65 per cent – of patients hospitalized with RSV have been four years old or younger. This age group also makes up the majority of ICU admissions due to RSV.

While elderly and young people, as well as those with other health conditions, may be at higher risk, Saxinger said it is important for everyone to protect against illness and get vaccinated to prevent more severe outcomes.

“All those things that we learned in COVID still hold true for RSV,” she told CTV News Edmonton.

In addition to hand washing and using masks, she highlighted staying home while sick.

“Staying home sick is something that I think we’re starting to kind of trend back towards what we used to do. And that’s not a good idea because any virus that spreads person to person a little bit more aggressively, we should try to prevent spreading that in schools and workplaces.”

Two general groups are eligible for the RSV vaccine in Alberta: pregnant and elderly people.

Year-over-year RSV data was not available.

With files from CTV News Edmonton’s Kyra Markov and Matt Woodman