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Health Canada has approved a new Pfizer vaccine, Abrysvo, to combat respiratory syncytial virus (RSV).
The vaccine is intended for newborns, from birth to six months of age, who would receive antibodies through maternal immunization, and for people over the age of 60 — both groups who are particularly vulnerable to RSV.
This news comes as a relief to pediatricians, who are flooded with admissions linked to RSV every winter.
"RSV is the leading cause of hospitalization in children under the age of one here in Canada," said Jesse Papenburg, pediatric infectious diseases specialist at the Montreal Children’s Hospital. "Peak hospitalization rates tend to occur in the second month of life. So really, the youngest babies are most vulnerable to severe disease."
For new and expecting mothers curious about the RSV vaccine and maternal immunization, Yahoo Canada spoke to an expert about what to expect.
What is RSV?
RSV is a common and contagious virus that primarily affects the respiratory system, particularly in young children. It can cause symptoms similar to a cold, such as coughing, sneezing, and a runny or stuffy nose.
While RSV is usually mild in healthy individuals, it can lead to more severe respiratory problems, especially in infants and older adults.
Papenburg said when a young infant encounters their first infection — when a child has no prior immunity to RSV—there's a greater likelihood the virus moves from the upper respiratory tract down into the lungs. Once in the lungs, RSV can cause bronchiolitis or pneumonia.
"And children with bronchitis or pneumonia, can have wheezing with their breathing, difficulty breathing, and some may require oxygen supplementation, or respiratory support or IV hydration," said Papenburg, adding that's what will lead to their hospitalization.
According to the Public Health Agency of Canada, the risk of severe outcomes from RSV infection is also higher among children with pre-existing conditions like chronic lung disease or compromised immune systems.
RSV also causes seasonal epidemics in Canada, with most cases occurring during winter.
Maternal immunization: How can I protect my newborn from RSV?
The single-shot Pfizer vaccine is approved for the third trimester of pregnancy, from 32 to 36 weeks.
For people aged 60 and above, the vaccine will also be a single shot.
Papenburg said that by giving the vaccine to a pregnant person, they will develop their antibody response in about two weeks.
From there, those antibodies will then cross the placenta and protect the baby during the first months of life when they're at greatest risk from severe disease.
"The baby's not producing their own antibodies," Papenburg said. "So it's what we call a passive immunization because it's really those antibodies from mom — that will, over time, degrade and no longer offer protection to the baby — but will have tide that baby over."
Maternal immunization is already recommended for other diseases, including influenza and COVID-19.
How can I get the new RSV vaccine?
According to Health Canada, federal authorities will collaborate with provincial and territorial counterparts to assess interest, demand and timelines for the RSV vaccination program.
Papenburg said we can expect the vaccinations in time for the next RSV season.
The National Advisory Committee on Immunization is also in the process of developing recommendations for the best use of the RSV vaccine, as well as a monoclonal antibody called nirsevimab.
The monoclonal antibody is one injection given either right after birth or in the first few months of life at the start of the RSV season. Though nirsevimab was approved by Health Canada in April 2023, there was no availability due to high demand in the U.S.
"The antibodies have been shown to offer protection for the first 150 days or so and reduce the risk of hospitalization," Papenburg said.
He added one main barrier that might prevent both the vaccine and the monoclonal antibody from being used or recommended universally, is the cost.
The vaccine is priced at more than $200 and the monoclonal antibody is around $950.
Papenburg said if Canadians can use these products in a universal vaccination program, there would be a noticeable difference for physicians working in child health during the winter months.
Is the Abrysvo RSV vaccine safe and are there risks?
The Centre for Disease Control and Prevention said side-effects for the person receiving the shot include:
Pain where the shot is given
According expert Papenburg, the newly approved vaccine and the monoclonal antibodies — both already being used in the U.S. and in Europe — are effective and safe.
"Both of these products are very different ways to reduce the burden of RSV on young children."
We know that both of them work, and both of them are safe.Dr. Jesse Papenburg
He explained studies included over 3,700 pregnant individuals that received the vaccine and over 3,700 that received placebo. It was observed that in these studies, more preterm births occurred among vaccine recipients than placebo recipients — 5.7 per cent versus 4.7 per cent.
"This difference was not statistically significant and the data are insufficient to establish a relationship with preterm birth," Papenburg claimed.
He added administration of the vaccine at 32-36 weeks' gestation is "thought to mitigate such risk if it does indeed exist" as there is less opportunity for preterm birth compared with the trial dosing interval of 24–36 weeks' gestation.