Previous studies suggest that per- and polyfluoroalkyl substances (PFAS) may act as immune suppressants. However, research about the impact of PFAS exposure on antibody responses to the measles, mumps, rubella (MMR) vaccine is limited and inconsistent.This report includes 748 mother-child pairs from the Boston Birth Cohort, with 8 PFAS compounds measured in maternal plasma shortly after delivery. IgG reactivities to measles and rubella were profiled in cord blood and venous blood plasma during early childhood, using Phage ImmunoPrecipitation Sequencing. Linear regression models were applied to assess the relationships between log2-transformed PFAS and IgG reactivities as measured by Viral Aggregate Reactivity score (VARscore, with inverse normal transformation) for measles and rubella. Quantile g-computation was applied to evaluate the PFAS mixture - VARscore associations.The detection rate for 8 PFAS compounds ranged from 90 % to 100 % in maternal plasma. Maternal PFAS burden score (P = 0.01), but not individual PFAS compounds, was associated with lower VARscore for measles in cord blood. In 348 children after receiving the MMR vaccine, three maternal PFAS compounds (Me-PFOSA-AcOH, PFHpS and PFHxS) were significantly associated with lower measles VARscore (P