Why most Canadians don't need another COVID-19 booster — at least not yet
Canadian, international guidance focuses on high-risk individuals. What about everyone else?
After several years of public health messaging calling on people to get multiple rounds of COVID-19 vaccines, you'd be forgiven for doing a double-take on some of the latest Canadian and international guidance around booster shots.
In short, it's that while vulnerable adults should get an additional dose this spring, the general population doesn't need to rush out for another round — and might not have to for a while.
The full picture, of course, is a bit more complicated. Someone's individual risk can shift quickly, such as becoming pregnant or acquiring an immunodeficiency, and even being low-risk for serious health issues from a SARS-CoV-2 infection doesn't mean no risk. This virus also remains somewhat unpredictable, and there's a chance it could still evolve in unexpected ways.
But, for now, this year's guidance marks a major shift in the global vaccination approach, at a time when a majority of the population has either been vaccinated, infected, or both.
"Right now we're at a very different place than we were, say, a year ago, or two years ago, or three years ago … our community immunity is very different," said Alyson Kelvin, a virologist and vaccine researcher with the University of Saskatchewan's Vaccine and Infectious Disease Organization.
The latest recommendations in Canada, out in early March from the National Advisory Committee on Immunization (NACI), call for another round of booster shots starting this spring for vulnerable adults, rather than the broader population.
The Canadians who should get another bivalent mRNA vaccine dose includes seniors 65 and older, those living in congregate settings such as long-term care, and any adults with moderately or severely compromised immune systems — at an interval of six months or so after someone's last infection or vaccination.
The World Health Organization later echoed that approach, stressing that high-risk groups should get a booster around six to 12 months after their last vaccine, while healthy kids and teens might not need a shot.
The U.S. is also expected to go the same route by approving another dose for seniors and individuals with weakened immune systems.
So, what about everybody else? Is the rest of society — millions of Canadian kids, teens, and younger adults — done with COVID-19 shots for good?
Not exactly.
WATCH | Experts recommend spring COVID-19 booster for at-risk groups:
Durable protection, but some remain more at risk
Scientists stress there's a specific level of risk associated with people whose immune systems are weaker, either because of their advanced age, or because of a condition like HIV/AIDS, or because they're on immune-suppressing drugs during cancer treatment or following an organ transplant.
People who didn't get a COVID-19 vaccine, or stopped after one or two doses in the early days of the vaccine rollout, could also be at risk of more serious illness — particularly those who still haven't been infected yet.
In those cases, medical experts are clear: Another shot this spring is a smart call.
"People who haven't had COVID and have underlying illness, or are over 65, really ought to get their second bivalent booster," said Dr. Allison McGeer, a researcher and infectious diseases specialist with Sinai Health System in Toronto.
Global guidance around COVID-19 shots is still focused on protecting people against serious illness and death, and preventing high levels of hospitalizations in health-care systems, she added, rather than mitigating more manageable infections in younger, healthier individuals.
And, for the bulk of the population, that protection against dire outcomes from COVID-19 does last for months.
Overall estimated vaccine effectiveness was "higher against severe outcomes compared with symptomatic infection and did not have the same degree of waning," noted one Ontario study on how COVID-19 vaccines fared against the Delta and — currently circulating — Omicron variants, which was published last year in the Journal of the American Medical Association.
Bivalent vaccines, which were designed to target the BA.4 and BA.5 Omicron subvariants, were also associated with a lower risk of severe infection with several later members of the Omicron family, researchers wrote in new correspondence in the New England Journal of Medicine.
"The effectiveness was higher against hospitalization and death than against infection and waned gradually from its peak over time," their letter continued.
"The vaccines continue to do a very good job providing durable or long lasting protection from severe outcomes," explained McMaster University immunologist Matthew Miller, the scientific director of the Michael G. DeGroote Institute for Infectious Disease Research.
"And that certainly extends at least out to nine months — and probably even further — since last vaccination or last exposure."
Dr. Donald Vinh, an associate professor in McGill University's faculty of medicine and health sciences, agreed the current data suggests months-long protection, in part from vaccines, but also through the potent combination of prior vaccination and infection for a growing number of Canadians.
One Canadian study, published in The Lancet Infectious Diseases in January, found that two doses of an mRNA vaccine, coupled with a prior Omicron infection, offered a strong shield against future infection from Omicron subvariants.
"You have hybrid immunity," Vinh said, "and there is a strong chance that you're protected against severe disease."
Your own risk level can shift
While it might be tempting to rest easy for the foreseeable future if you don't consider yourself high-risk, of if you've already had COVID-19 alongside several vaccine doses, there are other factors to consider when timing another shot — as protection can wane over time, while new variants may find fresh ways to slide by our immune system.
"Moving forward, you know, in six months, we might be in a totally different position with a different variant circulating," Kelvin warned.
Someone's personal risk level can also ebb and flow. Becoming pregnant, for instance, quickly puts someone at a much higher risk of severe COVID-19, including risks to the fetus as well, with Canadian research showing a 10 times higher risk of ICU admission.
Public Health Ontario lists pregnancy as a high-risk condition eligible for a spring booster, the latest guidance shows, and the World Health Organization is also calling for pregnant individuals to stay up-to-date on their shots.
"Pregnancy really is a game changer," said Vinh. "And we know that we've had near-catastrophic experiences here where women have nearly lost their babies or their lives because of COVID."
Scientists expect annual shots — eventually
For the general population, scientists who CBC News spoke to said they suspect COVID-19 vaccines for the broader population will eventually be recommended at an annual interval, assuming the virus settles into a more predictable, seasonal pattern, for a couple key reasons.
"One is that it lines up fairly well with where we start to see that protection against severe outcomes starting to wane," said Miller. "And secondly, it leverages an existing infrastructure for mass vaccination."
Even now, Vinh said, lower-risk Canadians who haven't had a shot at any point in the last year should still consider another round.
"If your last vaccine booster dose was 12 months ago or more, you really should be getting a vaccine booster dose regardless of your risk category because as we know, COVID-19 has not gone away — it very much is circulating," he said.
There's also a chance certain people will be hit hard by first-time infections, even if they're otherwise healthy.
And while vaccination is thought to lower the risk of developing long-lasting symptoms, more Canadians are still developing long COVID, whether that's a few months of frustrating impacts on someone's sense of smell, or years of debilitating fatigue and other health issues.
McGeer said it's understandable that younger adults may want an extra booster to reduce their risk of getting sick, or their risk of long COVID, or to try and avoid transmitting the virus to vulnerable adults in their life — even if those don't line up with public health priorities focusing on simply keeping people out of hospitals.
Going forward, several experts agreed, it's all about balancing people's desire to get additional shots with the data to back up the ideal approach.
"We don't want people to be overly zealous in their anxiety about getting up-to-date with their booster doses," said Vinh. "On the other hand, we don't want complacency either."
ABOUT THE AUTHOR
With files from Adam Miller
