This season’s flu shot targets two types of influenza A and one type of influenza B.Tara Walton/The Canadian Press
Question: I heard that this year’s flu shot isn’t a very good match for the virus. So, what’s the point of getting the annual jab?
Answer: You are not the only one who is having doubts about the value of the influenza vaccine – and that hesitancy is setting off alarm bells throughout the health care system.
“I worry about the number of questions and concerns that I have been hearing from my patients,” said Fahad Razak, an internal medicine physician at St. Michael’s Hospital in Toronto. He says he is trying his best to reassure patients that the vaccine can still help guard against the development of severe illness, even if it’s not a perfect match for the flu virus.
To better understand the protection provided by the vaccine, it’s worthwhile reviewing what is in it and how it works.
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The influenza vaccine is meant to prompt the immune system to be on the lookout for strains of the virus that experts think will be circulating during the coming flu season. Infectious disease experts keep track of emerging influenza strains through a global surveillance network. And each February, they decided what the next flu season’s vaccine will target, thereby providing manufacturers with sufficient time to create “over a billion doses,” said Dr. Razak, who is also an associate professor at the University of Toronto.
But the long production timeline increases the risk that the viral strains will change, or mutate, before the vaccine is injected into people’s arms.
This season’s flu shot targets two types of influenza A – known as H1N1 and H3N2 – and one type of influenza B.
Officials at the World Health Organization report that H3N2 has acquired several mutations in recent months, suggesting that this part of the vaccine may not be the best match for this particular strain of the virus.
Under ideal conditions, the vaccine stimulates the production of many antibodies that easily latch onto viral particles, said Dawn Bowdish, an immunologist and professor of medicine at McMaster University in Hamilton.
Antibodies, one of the immune system’s first lines of defence, will either neutralize the virus or mark it for destruction by other immune cells.
“When it’s an imperfect match, the antibodies don’t really stick very well to the virus,” Dr. Bowdish explained.
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So, some of the viruses will enter the body’s cells where they will start producing copies of themselves. The copies are then released into the body, causing various degrees of illness.
However, Dr. Bowdish noted that the vaccine doesn’t just boost antibody levels. “It’s not an all or nothing approach.” Other parts of the immune system, such as T cells, can identify infected cells and eliminate them. What’s more, she says the vaccine modifies the “disease process” in various ways that reduce the overall severity of the illness.
“We know that people who get vaccinated, even in years when it is not a perfect match, still end up getting less sick and they are less likely to be hospitalized or die.”
She also pointed out that the H1N1 and influenza B antibodies made in response to the vaccine appear to be very effective according to preliminary data. “This is particularly good news for children and young people who are more likely to get seriously ill with these strains if they are not vaccinated.”
Meanwhile, laboratory-confirmed cases of influenza are already on the rise in Canada. Now would be the prime time to receive the shot, said Dr. Razak. It usually takes up to two weeks to stimulate the immune system to get the full benefit of the inoculation.
“This is a vaccine for anyone over the age of six months, and it is especially important for those who are at higher risk of complications from the flu,” said Dr. Razak. This includes older adults, the very young, pregnant women and people with underlying medical conditions.
Canadian public-health officials are concerned that we could be in for a very rough ride based on the influenza season that just ended in the Southern Hemisphere, which often serves as a harbinger of what will happen here. Data show that Australia had a really bad flu season with a higher than usual level of hospitalizations.
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Canadian officials are also worried about declining vaccination rates among some segments of the population. And news of the mismatched flu vaccine could be another disincentive to get the shot.
But Dr. Bowdish sees reason for optimism at least among seniors. She noted that 73 per cent of those 65 and older got the flu shot last year. “That is a bit less than our target of 80 per cent, but it is consistent with prepandemic years,” she said. “Our older adults are still committed to getting the flu shot.”
Even so, if a lot of other people need medical care for the flu, that would put an additional burden on Canada’s already stretched health care system.
Dr. Razak said about two-thirds of all adults who end up in hospital with severe influenza complications have not received a flu vaccination – and 90 per cent of children hospitalized for flu are also unvaccinated.
“I see this as is a tragedy because it’s a vaccine-preventable illness,” said Dr. Razak. “By getting the flu vaccine, you’re doing your part to protect our hospitals, as well as your own health.”
Paul Taylor is a former Patient Navigation Adviser at Sunnybrook Health Sciences Centre and former health editor of The Globe and Mail.