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The National Advisory Committee on Immunization (NACI) released its recommendations last week and advised that Canadians at risk of severe illness due to COVID-19 should get an additional booster dose this spring.Lars Hagberg/The Canadian Press

Question: Why isn’t everyone being offered a COVID vaccine booster shot this spring?

Answer: Unlike previous COVID-19 vaccination campaigns, which were open to the general population, the next round of shots will probably be limited to people at risk of developing severe disease if they become infected with the virus that causes COVID.

Severe disease is a concern because these individuals may require a hospital stay, putting an additional burden on the health-care system, and it could even result in their death.

According to the National Advisory Committee on Immunization (NACI), which produced the new recommendations for booster shots, high-risk individuals include:

· People aged 80 and older;

· Adult residents of long-term care homes;

· People with complex medical care needs in congregate living settings;

· Those 18 years and older who have weakened or compromised immune systems due to either medical treatment or an underlying health condition; and

· Those aged 65 to 79, particularly if they have no history of a previous COVID infection.

NACI released its recommendations last week, roughly six months after the last booster program was rolled out.

The timing is important because protection from COVID vaccines tends to wane after about six months, said Fahad Razak, a professor in the Temerty Faculty of Medicine at the University of Toronto and an internal medicine physician at Toronto’s St. Michael’s Hospital.

Back in September, Canadians were offered a new type of “bivalent” vaccine that guards against the original COVID virus and the highly transmissible Omicron variant.

Now, those who were first in line for the bivalent doses can expect dwindling protection from their last inoculation.

That waning immunity poses a greater risk to some groups than others, Dr. Razak said.

He noted that during the pandemic many people have acquired a degree of immunity to the virus, either through vaccinations or infections. And some have had both vaccines and infections, which produces what’s known as “hybrid” immunity.

“Evidence from multiple studies suggests hybrid immunity may give you stronger and more durable protection than infection alone or immunization alone.”

For healthy young people, waning protection at the six-month mark “won’t make that big of a difference because their baseline risk for severe disease is very low,” Dr. Razak said.

However, for older adults and those who are immune compromised, that decline in vaccine effectiveness could lead to an infection that lands them in hospital.

This is the basis of NACI’s rationale in recommending that high-risk individuals may get a repeat of the bivalent dose to ensure that they have continued protection.

Not everyone in the medical community agrees with the limited scope of the proposed booster program, which will be implemented as each of the provinces and territories sees fit.

“I think these recommendations are based on the hope that things will get better with the rising level of population immunity,” said Allison McGeer, an infectious disease physician at Sinai Health System in Toronto.

But she pointed out that viral particles found in municipal waste water samples suggest there’s still a fairly constant transmission of the virus in the community. “And a substantial number of hospitalizations and deaths are continuing to occur.”

What’s more, over the past year numerous Omicron subvariants have emerged and some are even better at evading the immune system’s defences than their predecessors.

And as many people are abandoning most precautions, including wearing masks, on the assumption that the pandemic is over, this increases the likelihood they will encounter the virus.

“As older adults continue to get infected, we are going to see more hospitalizations and deaths in this group,” Dr. McGeer predicts.

She thinks NACI should have used much stronger wording in its booster-shot recommendations for people in the high-risk groups. NACI simply said they “may be offered” a vaccine, rather than specifically stating they “should get” a shot.

“In my opinion, if you’re 65 and older and it’s been six months since you’ve had an infection or your last booster, you should get another dose of the vaccine,” she said. The extra boost means “you will get less severe disease if you’re infected.”

Still other experts believe NACI should have recommended booster shots for virtually everyone – not just those considered at higher risk.

“My concern is that the focus has been on keeping the most vulnerable people out of hospitals instead of preventing long-term health consequences,” said Dawn Bowdish, a professor of medicine and a Canada Research Chair in Aging and Immunity at McMaster University in Hamilton.

She said infected young people may not get sick enough to end up in hospital, but some of them could be left with lingering health problems.

One potential side effect is long COVID, in which symptoms persist for an extended period, Dr. Bowdish said.

She added that a booster program that includes everyone would also help bring down the amount of virus circulating in society. “If we don’t reduce the total burden of infections, it means the virus just has more opportunities to find people who are vulnerable.”

Some medical experts anticipate that COVID vaccinations eventually will be administered only once a year – similar to the annual flu shot. But such speculation is “just wishful,” said Dr. Bowdish.

“We are now seeing peaks in cases roughly every three months and there is no reason to believe that this trend will change any time soon,” she explained. “So, moving toward fewer vaccine campaigns probably isn’t a good strategy.”

In a statement released with its latest recommendations, NACI said it continues to monitor the rapidly evolving scientific data “recognizing that the trajectory of the COVID-19 pandemic remains unclear.” It added that “updated recommendations will be made as needed.”

For now, NACI has placed the priority on higher-risk groups. But should a new and highly transmissible variant emerge, “we may have to expand vaccinations again to all people,” Dr. Razak said.

Paul Taylor is a former Patient Navigation Adviser at Sunnybrook Health Sciences Centre and former health editor of The Globe and Mail.

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