2026 Update in Maternal Immunization

Abstract

Maternal immunization plays a critical role in reducing the severity of infectious diseases in pregnant women and providing  protection to infants during the first six months of life through transplacental antibody transfer. The efficiency of antibody transfer depends on maternal antibody levels, placental transport mechanisms, and the timing of vaccination during pregnancy. Typically, 2–4 weeks are required for antibody generation following vaccination, with an additional 3-6 weeks needed for effective transfer to the fetus. As postnatal antibody transfer through breast milk provides lower protection, appropriate timing of maternal immunization appears pivotal. According to the 2025 Thai Guidelines, four vaccines are recommended for use during pregnancy: influenza, COVID-19, pertussis, and respiratory syncytial virus (RSV) vaccines. Influenza and COVID-19 vaccines are recommended from at least 12 weeks of gestation, pertussis vaccination is advised between 20 and 32 weeks, and RSV vaccination between 24 and 36 weeks of gestation. Clinical evidence demonstrates that these vaccines significantly reduce severe maternal infection, infant hospitalization, ICU admission, and mortality. Due to the low incidence of severe COVID-19 cases and low protection to new variant COVID-19 pathogens of the vaccine, the COVID-19 vaccine should be considered only in high-risk pregnancies and is currently removed from the routine vaccination practice in Thailand. Maternal vaccination against pertussis has been shown to substantially reduce laboratory-confirmed pertussis in infants, while maternal RSV vaccination has demonstrated high efficacy in preventing severe RSV-associated lower respiratory tract infection in infants up to six months of age. Despite strong evidence supporting vaccine efficacy and safety, challenges remain, particularly regarding vaccine cost and accessibility. While several vaccines are included in national immunization programs, others require out-of-pocket payment, which may limit uptake. Integrating maternal immunization into routine antenatal care, accompanied by clear communication from healthcare professionals, is essential to vaccine acceptance and maternal and infant health outcomes.