Maternal immunization is recommended through transplacental antibody transfer to protect newborn babies against respiratory syncytial virus (RSV) and pertussis. The objective of the study is to realize the current situation of maternal transfer of antibodies against RSV and pertussis before introduction of RSV maternal vaccine.

Maternal serum samples were taken from 421 pregnant women before delivery, and 366 paired umbilical cord blood samples were obtained. Pertussis toxin (PT) antibodies and neutralizing test (NT) antibodies against RSV were examined. Follow-up serum samples were obtained from 22 infants at 2 and 6 months, and one and 1.5 years after birth.

RSV NT antibody was positive in all maternal sera and showed higher levels in umbilical cord blood, with a 1.31-fold increase. It decreased to 1/3 levels at 2 months and 1/8–9 levels at 6 months after birth in comparison with umbilical blood. Three subjects were considered RSV infection between 2 and 6 months after birth. The positive rate of PT antibody was approximately 30 % in pregnant women with extremely low levels, which decreased to undetectable at 2 months, increased at 6 months with routine immunization, decreased at one year, and increased at 1.5 years with a booster dose of pertussis-containing vaccine.

The transplacental transfer ratio was 1.31 for both RSV and pertussis antibodies. Transferred RSV NT decreased to 1/3 levels at 2 months and 1/8–9 levels at 6 months. PT antibody levels were undetectable until 2 months. The data suggests the critical role of maternal immunization.

Pertussis PT

Respiratory syncytial virus (RSV)

Transplacental transfer

Umbilical cord blood

© 2025 Japanese Society of Chemotherapy, Japanese Association for Infectious Diseases, and Japanese Society for Infection Prevention and Control. Published by Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.