While doctors fear a lacklustre response from the public to more boosters, some experts outside Canada are questioning the need for an expansive round of boosting
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Canada’s vaccine advisors are recommending a COVID-19 booster dose of yet another reformulated vaccine this fall. It may prove a tough sell.
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With uptake diminishing, dose after dose, COVID vaccines may be approaching “sort of an acceptability settling point,” immunologist Dr. Matthew Tunis, executive secretary to the National Advisory Committee on Immunization (NACI), said in an interview with National Post.
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Additional “promotional activities” and communication strategies may be needed, he said, “to explain and rationalize what value the vaccine program can bring.”
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Others also fear a lacklustre response. “My worry is that we will have very low uptake of vaccines in the fall,” said Dr. Fahad Razak, an internist with Unity Health in Toronto and a past scientific director of Ontario’s COVID-19 scientific advisory table.
However, some experts outside Canada are questioning the need for an expansive round of boosting. “I believe we should stop trying to prevent all symptomatic infections in healthy, young people by boosting them with vaccines containing mRNA strains that might disappear a few months later,” pediatrician Dr. Paul Offit, a member of the U.S. Food and Drug Administration’s vaccine advisory committee, wrote in the influential New England Journal of Medicine earlier this year.
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Boosters are probably “best reserved” for high-risk groups, Offit said, like the elderly and immunocompromised. The level of neutralizing antibodies doesn’t tell the whole story, he said. Human T cell defence, cellular immunity, appears to be coping with SARS-CoV-2 mutations, Offit said in an email to the National Post.
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“The good news is that the epitopes (parts of the spike protein) recognized by T cells, which are critical in protection against severe disease, have remained relatively well conserved,” Offit said.
“So, even if you were only vaccinated with the original ancestral strain, protection against severe disease in those who are relatively young and healthy appears to be holding up.”
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Not everyone agrees with him. SARS-CoV-2 “has evolved dramatically in the last three years,” Razak said. “The mutations that have emerged in many ways makes the virus nearly unrecognizable to the immune system, and to the protections we had in place against the original variant.”
The “who to boost” debate comes as a sizable proportion of the Canadian population already appears booster weary. While 83 per cent of the population has received at least two doses of a COVID vaccine, just over half — 51.5 per cent — are “fully vaccinated” with a third dose, according to the COVID-19 Vaccination Tracker.
Only about 26 per cent of Canadians aged five and older received one of the bivalent vaccines that rolled out last September — a 50-50 mix that contained some of the original strain, plus the then-rapidly spreading Omicron subvariants BA.4 and BA.5.
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Razak said that if someone is eligible for a booster — they’re six months or more out from their last vaccine or last COVID infection — “don’t go out and get vaccinated now, unless you have a specific, high-risk reason to do so.” Instead, he said people should wait until the updated shots are available in the fall, when peak circulation of the virus is expected.
The latest formulations, now under review by Health Canada, have dropped the original strain entirely, which is essentially extinct, no longer circulating in humans. They target newer Omicron subvariants, specifically the dominant circulating strain XBB.
“Individuals vaccinated with the updated formulation are expected to benefit from a better immune response against these variants compared to current vaccines,” NACI said in its latest advice.
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Starting in the fall, for those previously vaccinated against COVID-19, NACI recommends a dose of the new vaccines for people in whichever age groups are ultimately authorized, if it’s been at least six months from the previous COVID vaccine or known SARS-CoV-2 infection, “whichever is later.”
Immunization is particularly important for those at increased risk of severe disease, NACI said.
Immunity from even hybrid protection — vaccination plus infections — wanes with time, NACI said.
The best way to protect the vulnerable “is to have everyone boosted,” said McMaster University immunologist Dawn Bowdish.
There isn’t a health system in Canada that isn’t struggling currently, with COVID circulating at low levels, Bowdish said. “It’s imperative we get vaccinated so that during cold and flu season we don’t see the same disruptions to health care that we saw last year.”
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Part of the problem is calling them “boosters,” she said, suggesting people are getting a “top up.” Like a yearly flu shot, “you can’t reasonably expect to be protected from symptomatic infections or hospitalization unless you are recently vaccinated with a matched vaccine.”
Ultimately it will be up to the provinces and territories to decide on a fall roll-out.
In Canada, rates of hospitalizations and deaths are highest for the 60 and older, and highest still among those 80 and older “and those who are unvaccinated,” NACI said. Rates are lowest for those recently vaccinated, and those with hybrid immunity (a combination of immunity from vaccinations and infections), particularly if the previous infection was with an Omicron strain.
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Most Canadians have already contracted COVID. Data from blood donors suggest nearly 80 per cent of the population overall had infection-acquired antibodies in May. The vast majority were infected with Omicron.
COVID isn’t the unpredictable, severe respiratory illness it once was. Overwhelming COVID pneumonias, where people rapidly deteriorated, requiring high levels of oxygen, many of them dying, “are very, very rare now,” Razak said.
Infections that don’t land people in hospital “can still be very disruptive,” he said. They can be the “tip over” event, exacerbating heart failure or other chronic illnesses. “We are trying to move towards this position of having a stable, post-pandemic period for Canada…. We want to live the healthiest, least disruptive lives possible,” Razak said.
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There is “nothing that I have seen scientifically,” he said, to suggest that the immune system can become exhausted by repeated exposures to the vaccines.
There’s been a “consistent trend” of waning protection from the vaccines, Tunis said, “and we’re still early in our understanding of hybrid immunity,” including how hybrid immunity is performing in the XBB era, he said.
“We’re not at a point yet in the evolution of the science around this pandemic where we can really proclaim with certainty that hybrid immunity with a certain number of doses can protect you for X number of years,” Tunis said.
National Post
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