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People walk past a vaccine clinic during the COVID-19 pandemic in Mississauga, Ont., on April 13.Nathan Denette/The Canadian Press

Many health experts say they are increasingly concerned by the slow uptake of first booster shots across the country, warning that two doses of COVID-19 vaccines don’t offer sufficient protection against the Omicron variant and that many Canadians may be unknowingly at risk as a result.

Only 47 per cent of the population, or 57 per cent of those 18 and older, have received a booster shot so far, according to the Public Health Agency of Canada. This is a growing concern, experts say, because mounting evidence shows that three mRNA COVID-19 vaccinations are necessary to provide adequate protection against the Omicron variant.

“This is a minimum three-dose vaccine,” said Katharine Smart, president of the Canadian Medical Association. “We haven’t got everyone over that finish line. For some people, that’s going to mean they die.”

Dr. Smart said governments and health agencies have not done a good enough job highlighting the importance of first booster shots, and that standing by a podium repeating the same message is “not doing anything” and even irritating some.

“In the noise, we’ve lost people,” she said.

This week, Health Canada reported that nearly 1.5 million COVID-19 vaccines have expired since January, indicating that uptake of both primary series shots and boosters has experienced major decline.

Complicating matters is the fact that the National Advisory Committee on Immunization last week urged jurisdictions to focus on the “rapid deployment” of second booster shots to high-risk individuals, including older seniors in the community and all long-term care residents. While second boosters are important to protect those vulnerable individuals, some experts say they’re becoming more concerned about the consequences of so many not receiving their first booster.

“It is three shots to protect against Omicron,” said Brian Conway, president and medical director of the Vancouver Infectious Diseases Centre. “If we are going to tell people they need a fourth shot, the people who haven’t received a third shot will be even further behind.”

The issue of booster doses is critical because the now-dominant Omicron variant is able to evade some of the protective effect offered by two doses of the currently available mRNA vaccines, particularly in more vulnerable individuals. While third and fourth doses, or booster shots, don’t always stop people from becoming infected, they work very well at preventing hospitalization and death. For instance, a U.S. study published in the British Medical Journal in March found two doses of an mRNA vaccine was only 65 per cent effective at preventing Omicron-related hospitalizations in people 18 and older. For people who received three doses, the effectiveness at preventing hospitalizations increased to 86 per cent.

In light of the new surge of COVID-19 cases across Canada, this week, NACI strengthened its recommendation for first booster shots, saying adults 18 and older should be offered an additional mRNA vaccine at least six months after the completion of their last dose. (Recommendations for vaccination timing vary depending on age, health status and prior COVID-19 vaccines and infection. For many healthy adults, a first booster would be a third dose of an mRNA vaccine.)

But some say in order to get more people to line up, official communication about the importance of boosters needs to change.

“I think it really behooves us to get serious,” Dr. Smart said. “Where do we go from here with our health communication?”

Dr. Conway said some people may feel fatigued or disillusioned as advice on vaccine schedules seems to keep changing. But the SARS‑CoV‑2 virus is changing and as scientific understanding of vaccine protectiveness evolves, so must public-health guidance, he said.

The best available evidence suggests that three and, in some individuals, four mRNA doses, offer the best protection. A study published in the New England Journal of Medicine last week found that people 60 and older who received a second booster shot were less likely to experience severe COVID-19 outcomes compared to people who only received one booster dose.

Because the Omicron variant is still so new, it’s unclear how long the protection against severe outcomes will last. But most health experts agree that it’s likely people will be offered boosters on a regular basis, possibly similar to annual influenza vaccination campaigns.

Many experts are also urging the Public Health Agency and other health organizations to stop using the term “fully vaccinated” to refer to those who have received two doses of an mRNA COVID-19 vaccine.

“I don’t think it’s a term that scientifically works or practically works,” said Doug Manuel, a senior scientist at the Ottawa Hospital Research Institute and a member of the Coronavirus Variants Rapid Response Network. “I think it’s misleading. I think it’s incorrect.”

When asked if the Public Health Agency is going to discontinue the use of the term “fully vaccinated,” a spokesperson sent an excerpt from a news conference this week during which Canada’s Chief Public Health Officer Theresa Tam said it’s a continuing discussion.

With a report from The Canadian Press

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