A new study suggests that maternal antibodies passed to babies in the last trimester of pregnancy may actually interfere with the infant's own immune response to vaccines administered in the first few months of life.
The study, titled "The Influence of Maternally Derived Antibody and Infant Age at Vaccination on Infant Vaccines Responses" and published in JAMA Pediatrics, found that high levels of maternal antibodies lingering in the infant at the time of immunization reduced their response to those vaccines.
"It is advisable to review and update vaccination status at the beginning of pregnancy and all women should follow their physician's advice on immunization strategies," Merryn Voysey, senior statistician and NIHR Doctoral Research Fellow at the Nuffield Department of Primary Care Health Services at the University of Oxford and study co-author, told Medical Economics. "Current vaccination policies are safe and effective. Our report provides important data that may be used to model the impact of modifications to the timing of vaccinations, and identifies an important issue for consideration by researchers and policymakers in developing new vaccines."
The report notes that vaccine response was also influenced by the infant's age at the time of first vaccination. Immunization schedules vary depending on infant ages, and the passing of maternal antibodies after vaccination for certain diseases is well established in previous studies. However, inactivated vaccines that are often used during pregnancy--including tetanus, pertussis and hepatitis B--may increase maternal antibodies while weakening the infant's own immune response to their own vaccination, according to the report.
The level of antibodies transferred through the placenta during the third trimester is dependent on a number of factors, including gestational age at birth, how well the placenta was functioning, and the mother's own serum antibody levels. After delivery, any antibodies transferred to the infant start to wane, but the process can take weeks to months depending on the level of antibodies initially transferred.
Many countries now encourage maternal vaccines like Dtap during the third trimester to protect infants until they can receive their own vaccine. The study authors suggest that this practice could "leave children more susceptible to disease later in infancy and increase transmission rates to unvaccinated cohorts."