Health Canada has approved a new antibody drug to help protect babies from serious illness caused by respiratory syncytial virus, or RSV.

Nirsevimab, also known by its brand name Beyfortus, was legal on April 19. It was developed by AstraZeneca and Sanofi.

Nirsevimab is “a monoclonal antibody to prevent serious lower respiratory tract disease caused by respiratory syncytial virus (RSV) infection in newborns and infants during their first RSV season,” Health Canada spokesman Mark Johnson said in an email to The Canadian Press on Friday.

The drug, which is given by injection, is also legal for children up to two years of age if they are at risk of serious infection, he said.

Monoclonal antibodies are made in a laboratory to mimic natural antibodies to prevent or treat diseases.

A picture of the respiratory syncytial virus taken via electron micrograph.
An electron micrograph of respiratory syncytial virus, also known as RSV. (CDC/The Associated Press)

‘Game-changer,’ says pediatric specialist

Nirsevimab attaches to a protein on the surface of the virus and hinders its ability to enter the body’s cells, especially those in the lungs, according to the European Medicines Agency, a regulatory body that last fall approved the drug for use in the European Union.

Canada already offers the monoclonal antibody palivizumab — also known by the brand name Synagis — to premature babies because they are more vulnerable to serious illness from RSV. The National Advisory Committee on Immunization (NACI) does not recommend palivizumab for healthy babies.

Palivizumab has to be injected about once a month — up to four times — during the RSV season to remain effective. Nirsevimab requires only one dose that lasts the entire RSV season.

“It’s a game-changer,” said Dr. Anna Banerji, a pediatric infectious disease specialist at the University of Toronto’s Dalla Lana School of Public Health.

Inuit babies in Nunavut are particularly hard-hit by the RSV, Banerji said.

Many become seriously ill each year and have to be transported out of remote communities to hospitals in the south, he said.

A one-dose drug could prevent many of those cases from happening, Banerji said.

‘Limited use’ expected in 2023/24 season

Although Health Canada has authorized nirsevimab for all infants, it’s not known whether it will be that widely administered.

It’s up to the provinces and territories to determine who gets the injections, often based on recommendations from the Canadian Agency for Drugs and Technologies in Health (CADTH).

Health Canada said that pending CADTH’s recommendations, it expects nirsevimab “will be available for limited use during the 2023/2024 fall/winter respiratory season.”

On Friday, the CADTH website said its review of how cost-effective nirsevimab is for RSV in infants is “in progress.”

Banerji said it’s vital that nirsevimab be offered to all Inuit infants in Nunavut — not just those who were born prematurely as is currently being done with palivizumab — because of their heightened risk and limited access to care if they get very sick.

Preventing medevacs would offset the financial cost of providing nirsevimab to more infants, she said.

Most children in Canada are infected with RSV by the age of two, according to the Public Health Agency of Canada’s website. It usually causes mild illness, but can be serious and is a common cause of bronchiolitis and pneumonia, the website says.

Last fall and winter, RSV, together with influenza and COVID-19, caused a surge in pediatric hospitals. Infectious disease experts say that was partly due to the lifting of pandemic restrictions, which had prevented respiratory infections in the previous year, so children were exposed to RSV for the first time.