INFLUENZA poses significant risks to young infants and pregnant women, leading to substantial illness and hospitalisations. In some winters, up to nine percent of infants under six months require medical care for influenza-related illnesses. Pregnant women are also at higher risk, particularly during pandemics like the 2009 H1N1 outbreak, which disproportionately affected this group.
Maternal influenza vaccination significantly reduces adverse outcomes, including maternal mortality, prematurity, and low birth weight. It also decreases influenza-associated hospitalisations and illness in both mothers and infants. Given these benefits, health authorities recommend influenza vaccination during any trimester of pregnancy.
Two types of vaccines are available postpartum: the trivalent inactivated vaccine (TIV) and the live attenuated influenza vaccine (LAIV). While both are considered safe for breastfeeding mothers, limited guidance exists on which offers superior protection for infants. Recent research comparing immune responses in postpartum women who received either TIV or LAIV found that TIV recipients had higher levels of breast milk IgG and serum IgG, with stronger IgA responses against H1N1.
Beyond antibody transfer through the placenta, breastfeeding may further enhance infant protection. Infants consuming milk from vaccinated mothers experience fewer respiratory illnesses with fever, suggesting local mucosal immunity. Systems vaccinology research is now investigating the immune mechanisms behind breast milk-mediated protection, analysing gene expression in breast milk and blood cells after postpartum vaccination.
Findings suggest that LAIV induces a stronger innate immune response in breast milk, while TIV generates higher adaptive immune responses. The delayed and sustained immune activity seen with LAIV could influence prolonged infant immunity, though more research is needed.
Maternal influenza vaccination remains a critical tool for safeguarding both mothers and infants. Ongoing research will refine vaccine recommendations, ensuring the most effective protection for this vulnerable population.
Reference
Schlaudecker EP et al. Transcriptome analysis in human breast milk and blood in a randomized trial after inactivated or attenuated influenza immunization. NPJ Vaccines. 2025;10(1):53.
