Most RSV infections are in babies less than 1 year old. But protection remains out of reach for many

Most positive tests for RSV so far this season in Canada have been among the youngest, federal data says. And while Health Canada has approved an immunization that can protect all babies from the illness, it's only available in a few jurisdictions.

For the week ending Nov. 30, about 51 per cent of RSV cases were in those one year of age and under, among those with age information.

RSV usually causes a minor cold, but it can cause severe illness in vulnerable groups. Older adults and newborns are among those most at risk, and it's a leading cause of seasonal hospitalizations each winter for children in Canada.

About 10 per cent of all hospitalizations due to RSV require pediatric intensive care, said Dr. Jesse Papenburg, a pediatric infectious disease specialist at the Montreal Children's Hospital.

Nirsevimab is made by AstraZeneca and distributed in Canada by Sanofi, under the name Beyfortus. The single injection protects infants through the fall and winter when RSV circulates regularly (as well as for toddlers, who remain particularly vulnerable the following season). It includes lab-made monoclonal antibodies.

But only Ontario, Quebec and the territories have negotiated contracts to offer it for free to all infants.

Hannah Markham lives in Nova Scotia, where only high-risk infants are eligible to receive the injection. The Halifax mother says she's anxious for her four-month-old this RSV season.

"For many Nova Scotian parents like myself, I think we're left feeling crestfallen," Markham said. "We want what other parents have, which is the opportunity to protect our children."

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Building toward universal program

This week, researchers from the U.S. Centers for Disease Control and Prevention found that nirsevimab was effective in reducing RSV-related hospitalizations in children under five years old.

Monoclonal antibody injections like nirsevimab give antibodies directly to a person, a shortcut to protection. Vaccines, meanwhile, prompt the person's immune system to make the antibodies and remember them in case of a future attack.

Provinces currently offer palivizumab (sold as Synagis) for high-risk infants, such as those born pre-term. The older monoclonal antibody is given on a monthly basis, while nirsevimab is a single dose.

This illustration provided by AstraZeneca depicts U.S. packaging for nirsevimab. (AstraZeneca/The Associated Press)

However, many lower-risk babies don't have access to either protection.

The National Advisory Committee on Immunization (NACI), which advises the federal government, decided in May not to recommend nirsevimab for all infants in the country at its current Canadian list price of $952.

Instead, it said to prioritize higher-risk infants for now, like premature babies, and eventually work toward "a universal RSV immunization program for all infants."

The shot can reduce hospitalization risk from RSV by 80%

Canadian pediatricians say they're hopeful the shot can help prevent RSV infections in babies here.

"It reduces the risk of hospitalization due to RSV by roughly 80 per cent," said Papenburg, "not only in the clinical trials, but that's also been observed in places like the United States, France and Spain that used the product last year."

Monoclonal antibodies like nirsevimab are "particularly useful in the scenario of RSV, where we know that the risk is greatest during those first few months of life," he said.

Dr. Filippe Scerbo, chief of pediatrics at Mackenzie Health in Vaughan, Ont., said the hospital has seen twice as many pediatric admissions for RSV compared with the previous month.

Dr. Filippe Scerbo is seeing more pediatric admissions for RSV at the moment. (Turgut Yeter/CBC)

"Those with more severe disease may have things like wheezing, some difficulty breathing," Scerbo said. "They may look distressed or incredibly tired. They may have difficulty eating or drinking."

Sanofi, the distributor in Canada, said six in 10 infants have access to RSV prevention with the injection, and the company is committed to supporting broad immunization.

"Sanofi continues to work with all provinces and territories, as they make decisions on their immunization programs, to facilitate access to Beyfortus for all Canadian babies for 2025 and beyond," a spokesperson told CBC News.

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Papenburg, who is also an associate pediatrics professor at McGill University, said he expects that the immunization will be widely available nationwide within the next year or two.

"It's unfortunate that we have this disparity — or I would say even to a certain degree, inequity — across provinces due to the way that the contracts were negotiated for this first season," Papenburg said.

The Sanofi spokesperson said they couldn't comment on prices negotiated by the provinces and territories, due to confidentiality.

Encouraging uptake

Papenburg said tens of thousands of doses of nirsevimab have been administered in Quebec, though data on uptake isn't yet available.

"We're seeing the best uptake when families have been informed about this product prior to the delivery" of the baby, he said.

From Nov. 1 to Dec. 11, Mackenzie Health delivered 244 doses at its two hospital sites in Richmond Hill and Vaughan — a 67 per cent uptake rate among parents who were asked if they'd like to have their child immunized for RSV.

An official with Ontario's Ministry of Health said 110,000 doses of nirsevimab have been distributed. Uptake figures are not yet available.

As a mother, Markham recognizes that what might be a sniffle in a healthy adult could be very detrimental in a baby. Markham said she's using hand hygiene and distancing when unwell to try to protect her first child as much as possible.