What is the rsv shot for babies and how does it work?

What the evidence says

The RSV shot for babies is a bit different from a normal vaccine. Instead of teaching the baby's own immune system to make antibodies, it gives the baby ready-made antibodies, proteins the body uses to fight germs, that were made in a lab. This is called a monoclonal antibody, and in Canada the two approved ones are nirsevimab (brand name Beyfortus) and clesrovimab (brand name Enflonsia).

These antibodies work by locking onto a part of the RSV virus called the fusion protein, which the virus needs to get inside cells and spread. By blocking this protein, the antibody stops the virus from infecting the baby's airway cells before it can make the baby sick.

Because the antibodies are given directly rather than the baby having to make them, protection starts right away after the single injection, unlike regular vaccines which can take a couple of weeks to work. This protection lasts for at least five months, which is usually enough to cover a whole RSV season.

In Canada, this antibody is recommended for all infants younger than 8 months during their first RSV season, especially if the birthing parent did not get the separate RSV vaccine during pregnancy. Children up to 24 months who have ongoing health risks, like chronic lung or heart conditions, may also get it going into their second RSV season.

There is also another option: a vaccine called RSVpreF can be given to the pregnant parent, which lets the parent's body make antibodies that cross the placenta to protect the baby after birth. Families usually choose one option or the other, not both, depending on timing and availability.