During pregnancy, when should the RSV vaccine be administered?

• A. 40-42 weeks
• B. 32-36 weeks
• C. 28-32 weeks
• D. 20-24 weeks

Answer: (B)

Vaccinate in the late second to early third trimester to maximize the transfer of protective antibodies to the baby. The main idea is that maternal RSV antibodies cross the placenta, and this transfer happens most efficiently in the later stages of pregnancy. Administering the vaccine around 32 to 36 weeks gestation provides high levels of maternal antibody that can be passed to the fetus just before birth, giving the newborn better protection during the first few months when RSV risk is highest.

If given too early, antibody levels in the baby at birth may have waned by the time the infant needs protection. If given too late, there may not be enough time for the mother to generate a robust antibody response and for the antibodies to cross the placenta before delivery. That’s why the recommended window is around 32–36 weeks gestation.