The relatively low circulation of the flu over the past two years puts young children at a higher-than-usual risk of catching it this fall and winter, experts say, who also fear that fewer pandemic measures and a reduction in vaccination spread even further.
To a lesser extent, adults’ resistance to the flu is also lower than it might otherwise be because fewer people got an immune boost from a recent winter infection, says infectious disease specialist Dr. Susy Hota , and stresses the added importance of flu shots this season.
“Our immune responses increase to some degree when we see these viruses more frequently,” said Hota, medical director of infection prevention and control at the University Health Network.
“We haven’t really had that for the last couple of years. So people could be more symptomatic and pick up these infections and notice them more over the next couple of years.”
Pandemic measures to limit the spread of COVID-19 resulted in only 69 confirmed flu cases in the 2020-2021 season and only sporadic cases in 2021-2022, according to a recent update from the National Immunization Advisory Committee, which advises the Public Health Agency of Canada. on the use of the vaccine.
The pool of potential flu patients this fall and winter is larger, just as masks and social distancing rules have dropped, says immunologist Dawn Bowdish of McMaster University in Hamilton.
“As a population we are ripe for the flu,” he said. “One of the reasons it seems to be spreading a little earlier than it would in a pre-COVID kind of year is because there are so many susceptible people who can harbor this infection.”
Like Hota, he says the potential increase in circulation in the coming months is “a very big problem” for children under the age of two who are exposed for the first time and are more susceptible to serious illness.
The same is likely true for three- and four-year-olds who might otherwise have gotten the flu as babies or toddlers but were spared because of COVID-19 mitigation strategies, he adds .
“Because we’re dealing with a lot of kids who haven’t had a lot of stimulation … we can expect that this year could be really problematic in young kids,” Bowdish said.
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He notes a similar scenario played out last summer when a surge in respiratory syncytial virus, or RSV, sent babies, toddlers and preschoolers to the hospital and strained pediatric health care resources.
While many other pressures continue to strain the health care system, including ongoing COVID-19 infections that many experts fear will also increase, it’s especially important to get a flu shot this year, Bowdish adds.
As for the flu risk to the general population, infectious disease expert Matthew Miller doesn’t expect a missed flu season to make us much more susceptible than previous years.
Miller, the director of McMaster’s Michael G. DeGroote Institute for Infectious Disease Research, says many adults may have some level of immunity built up from a lifetime of exposure to seasonal flu, including people grains that are generally not as strong as one. immune response in younger age groups.
This immunity can last for years and even decades if someone encounters a strain of flu that is closely related to something they’ve seen before.
“During the swine flu pandemic, older people were disproportionately protected from death because this virus closely resembled the virus that caused the 1918 Spanish flu,” said Miller, also an associate professor of biochemistry and biomedical sciences at McMaster .
“People who were very old and exposed to the Spanish flu of 1918 and similar viruses that circulated the year after that still had protection until 2009.”
There have been times when the same strain will recirculate for several years, but if it changes, that preexisting immunity becomes much less effective, Miller says.
Thanks to pandemic measures that also protected most people from getting the flu, Bowdish says the types of flu circulating now are quite different than before the COVID-19 outbreak.
“Because of all the social distancing (and) masking, many lineages of the flu virus have died out,” he said.
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Clues to this season’s dominant strain can be found in the one that circulated in the southern hemisphere, Miller says, noting that we can often expect to see the same version emerge in Canada.
“But that’s not always what happens in practice, because of course there are gaps between the Australian season and our season and the dominant virus can change in the meantime,” he said.
Still, Miller said it’s likely that someone who got sick in 2019 will have some protections this season, believing any changes to this year’s flu will be “modest.”
While countries like Australia, New Zealand and South Africa were particularly hard hit, Bowdish says it’s unclear whether that’s because the virus itself developed particularly problematic mutations, because vaccination rates fell short, or because the vaccine was not very well adapted to the strain.
Danielle Paes of the Canadian Pharmacists Association points to a survey of 1,500 adults in August that found only 50% of respondents said they would have a chance this year, down six points from a survey in 2021. The margin of error is more or less. 2.53 percentage points, 19 times out of 20.
Paes says waning interest in the flu shot could also exacerbate the impact of the flu this season.
A survey of 1,500 Canadian adults in August found that only 50% of respondents said they would have a chance this year, down six points from a survey in 2021. (Leah Hennel)
Hota points to the resumption of many pre-pandemic activities as the main factor driving flu infections this season, noting that mask mandates have fallen, people have resumed travel and are gathering indoors again.
“In previous years, we’ve had public health measures and some sort of restriction on people’s movement or socializing or people’s ability to congregate,” he said.
“This year is definitely different.”