Canada's vaccine advisers recommend RSV shots for infants

Pfizer Canada's vaccine RSVpreF (sold as under the name Abrysvo) is one of two shots now recommended by Canadian officials to ward off respiratory syncytial virus in infants.

Canada's vaccine advisory group said Friday it recommends building toward immunizing all infants from respiratory syncytial virus (RSV).

The common and highly contagious virus normally causes cold-like symptoms. But for more vulnerable populations such as infants and older adults, it can lead to more serious illness like pneumonia and bronchiolitis; a swelling of the small airway passages in the lungs.

RSV infects almost all children by the time they reach two years of age. It is also a leading cause of hospitalization in infants and young children.

In 2023, researchers reported nearly half of children hospitalized for RSV in Canada's pediatric hospitals in recent years were under six months of age. They called for preventative options to ease the pressure on intensive care units caring for the sickest.

Here are some key considerations in rolling out the shots.

What are the shots?

Pfizer Canada's vaccine RSVpreF (sold as Abrysvo), aims to prevent lower respiratory tract diseases caused by RSV, and was approved by Health Canada in January.

Sanofi's nirsevimab (sold as Beyfortus) is a monoclonal antibody to protect infants in their first RSV season — the fall and winter — as well as children who remain vulnerable to severe disease in the next season.

Who is it for?

The National Advisory Committee on Immunization (NACI) says the top priority for nirsevimab include:

• Infants entering, or born during, their first RSV season who are at increased risk of severe RSV disease, including those who are born at less than 37 weeks gestational age.
• Infants entering their second RSV season and who at ongoing increased risk of severe RSV disease due to preterm birth, chronic lung disease, severe immunodeficiency or other listed diseases.
• Infants entering, or born during, their first RSV season who would require complex transportation — such as an airlift — for severe RSV disease treatment, such as those from remote First Nations, Métis and Inuit communities. 

Depending on cost effectiveness, the group also recommends considering universal immunization with nirsevimab for any infant less than eight months of age entering or born during their first RSV season.

How do they work?

Nirsevimab contains proteins made in the laboratory to mimic the immune system's ability to fight off RSV, while RSVpreF is meant to protect infants in their first RSV season through passive immunity. When given in pregnancy, antibodies to fight the virus transfer to the fetus through the placenta.

NACI recommends that RSVpreF be considered as an individual decision together with information from the person's pregnancy care provider, in advance of, or during, the RSV season, to prevent severe RSV disease in their infant.

What happens next?

Provinces and territories need to decide on access, cost-effectiveness and affordability of rolling the products out to prioritized infants or all of them.

What about other at-risk populations?

Another RSV vaccine for seniors, from manufacturer GSK, was approved last August.