Is there any point in getting a flu shot that’s mismatched to the virus? Here’s what the science says

Influenza is rearing its head in Canada yet again, with the number of cases starting to rise on the heels of another tough flu season in the southern hemisphere.

Scientists are particularly watching the spread of a new form of the H3N2 strain that could be mismatched to this year’s vaccine.

That notorious form of influenza A is linked to more serious disease and recently gained mutations that could make the current flu shot less effective against it, CBC News recently reported.

So is there still a point in getting a flu shot this year? Medical experts say: absolutely. The latest shot offers plenty of protection against severe illness, and is particularly important for higher-risk groups. Here’s why.

Flu vaccine effectiveness can shift each season, since the virus itself is changing constantly.

There’s also a big difference between how well flu shots protect against simply getting infected in the first place, and the level of protection against serious illness and death.

“I think for most people, they’re not actually super worried about getting a sniffle or a cough. What they really want to make sure of is that they don’t end up in hospital,” Matthew Miller, an immunologist and researcher at McMaster University in Hamilton, Ont., told CBC News.

In October, Miller’s latest published research — a sweeping review of hundreds of prior studies on cases of infection in adults and children following a flu shot — showed these vaccines really work in the ways that matter most.

“We found that there was a really significant reduction in disease severity, and that was really reassuring, because it provides a high degree of confidence that there’s still great value in getting the vaccine,” Miller said.

Getting vaccinated can also curb virus transmission, helping stop the spread of flu to vulnerable groups such as older adults who are at a higher risk of death, noted Vancouver-based infectious disease specialist Dr. Brian Conway in a recent appearance on CBC’s Hanomansing Tonight.

New flu strain could hit infants, elderly hard | Hanomansing Tonight

Roughly nine in 10 Canadians who died of influenza and pneumonia in 2022 were aged 65 and up, Statistics Canada data shows, with more than half those deaths occurring among people aged 85 and older.

The bottom line? “You should run, not walk, and get the flu shot right now,” Conway said.

Canada’s National Advisory Committee on Immunization (NACI), made up of the country’s top vaccine advisors, says flu shots are particularly important for people at a higher risk, which can mean older adults, young children, people who are pregnant, and anyone with chronic underlying health conditions. 

“Influenza is a systemic disease,” said Conway. “You have fever, you have pains in your muscles, you have trouble getting out of bed at times, you can be short of breath. It can affect your lungs, it can lead to hospitalization, pneumonia, admission to the intensive care unit.”

Healthy, younger adults also get hit hard more often than you’d think.

More than one in 10 of all U.S. patients hospitalized with influenza last season did not have any underlying medical conditions, “highlighting that healthy individuals may also experience influenza-associated hospitalizations or complications,” noted a U.S. Centers for Disease Control and Prevention (CDC) report released in September.

In other words, everyone’s at risk from the flu. 

NACI officially recommends that flu shots “be offered annually to anyone six months of age and older who does not have a contraindication to the vaccine.”

As for babies, NACI stresses the need for vaccination during pregnancy to help transfer antibodies to protect newborns during their first months of life — when they’re “at high risk of complications from influenza infection, and too young to be immunized.”

Data shows being unvaccinated against the flu also leaves people at risk of serious illness.

Two-thirds of hospitalized patients in the U.S. during the last flu season weren’t vaccinated against influenza, U.S. CDC data shows, while a staggering 90 per cent of children who died from the virus weren’t fully vaccinated either. (Guidance stipulates that children up to the age of nine who have never had a flu vaccine before should receive two doses. After that, it’s given as a single, annual shot.)

“The sad reality is that those people who end up in hospital or in ICU or die every year… they didn’t know, in large part, they were at risk until it was too late,” said Miller, the McMaster immunologist. “… This is something that’s preventable [with a flu shot.]”

Canadian data from the last flu season, published in January in the journal Eurosurveillance, showed the risk of having influenza severe enough to require a doctor’s visit was cut in half for people who’d been vaccinated, compared to unvaccinated individuals.

While vaccine researchers are always trying to stay a step ahead of influenza, it’s hard to predict precisely how this fast-changing virus will evolve year to year.

This season is no different. As usual, this year’s annual flu shot aims to cover multiple bases, and features components that target various subtypes of influenza A — including strains of H1N1 and H3N2 — and influenza B. 

The good news: A recent CDC study found the latest vaccine formula cut flu-related hospitalizations by roughly half in southern hemisphere countries that already got through their flu seasons.

But the situation has changed since then. 

Alberta reports first flu death of season as experts warn of vaccine mismatch

Dr. Danuta Skowronski, epidemiology lead for influenza and emerging respiratory pathogens at the B.C. Centre for Disease Control, recently told CBC News that the southern hemisphere season was dominated largely by a form of H1N1, while more recently, H3N2 has been rising in various countries. 

The latest H3N2 strain is also acquiring mutations that widen the gap between what’s circulating and what’s in the current vaccine.

So, is it still worth getting this particular shot?

While a “mismatched” vaccine might be less effective against H3N2 in Canada this season, “the vaccine doesn’t just protect against one kind of influenza,” Skowronski said.

“For the coming season, though, H3N2 is likely to be a bigger player than it has been in the past few seasons,” she added.

Miller stressed that the possibility of a rise in H3N2 makes getting a flu shot all the more important to help keep patients out of Canada’s fragile hospital system.

“Even though it might not be a great match, its ability to prevent severe infection further reinforces the importance of getting vaccinated,” Miller said.