How do maternal vaccines protect newborn babies before they can be vaccinated themselves?

Some vaccines are given during pregnancy so the mother produces protective antibodies that can reach the baby before birth. These antibodies cross the placenta, especially in the later stages of pregnancy, and can also be passed through breast milk after delivery. This strategy is used to protect infants against diseases such as influenza, whooping cough and respiratory syncytial virus in some countries. It bridges the gap until the infant is old enough to receive their own vaccinations.