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When should my baby get the rsv shot under 3 months?

If your baby is under 3 months during RSV season (roughly fall through spring), they should get nirsevimab right after birth, ideally before leaving the hospital. If born before the season starts, the shot is given once the season begins.

Nirsevimab is a long-acting antibody, not a traditional vaccine, and protects immediately, so timing is built around the start of RSV season rather than a fixed infant age.

Strength of evidence

Strong

Multiple Canadian and international immunization guidelines (NACI, Canadian Immunization Guide, SickKids/AboutKidsHealth, AAP) directly address timing and agree with one another.

What the evidence says

The 'RSV shot' most babies under 3 months get in Canada is called nirsevimab (brand name Beyfortus). It isn't a regular vaccine that teaches the immune system to make its own defenses. Instead, it gives your baby ready-made antibodies that protect right away.

Because it works immediately, timing depends on when RSV season is happening, not on your baby's exact age. Canadian guidelines say nirsevimab should be given at the start of RSV season, since protection kicks in right away and there's no need to wait weeks like with a regular vaccine.

If your baby is born shortly before or during RSV season, doctors recommend giving the shot very early, sometimes before you even leave the hospital after birth. One source describes it as something that can be given any time after birth, including before going home, for babies under 8 months at the start of the season or those born during it.

If your baby was already born before RSV season starts (for example, born in spring or summer), the shot is usually given once the season begins in the fall, often around the 2, 4, or 6 month checkup, rather than right at birth. Supply may be prioritized for babies born during RSV season and for the youngest infants when the season starts.

Premature babies and babies with certain heart, lung, or immune conditions are a priority group and should get nirsevimab regardless of exact timing within the season. Talk to your baby's doctor or public health unit about when RSV season starts where you live and whether nirsevimab is available through your local program.

Sources

✓Reviewed by CH, MD, FRCPC

Reviewed by a specialist physician certified by the Royal College of Physicians and Surgeons of Canada, who has read this answer against the sources listed above and confirmed it reflects them. That is not medical advice about your child. How we review

Answer checked November 10, 2026

Educational information only. Not medical advice, not a diagnosis, and no doctor-patient relationship is created by using this. Founded Parent has not examined your child and does not know their history, so this may not apply to you. In an emergency, call your local emergency number. What Founded Parent cannot do

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