Partisan differences in childhood measles vaccination and general refusals: a retrospective cohort study of electronic health records in the United States, 1988–2024

Background: Vaccination remains one of the most effective public health tools globally. Yet recent years have seen increasing political polarization around vaccination, particularly in the United States, as well as measles outbreaks among unvaccinated children. Using individual-level data, we characterize the national evolution of parental political polarization in childhood vaccination refusal, timely receipt of a child's first measles, mumps, and rubella (MMR) dose, and delay in first MMR vaccination. Methods: = 27,475) party affiliation. We statistically test for increasing polarization over time across three outcomes: whether or not a patient had a documented vaccination refusal for any childhood vaccination, whether a patient received a timely first MMR dose, and the time delay to first MMR vaccination. Findings: < 0.01), or approximately 2.5 months over the study period. Interpretation: This study provides the first nationwide, individual-level evidence linking parental political affiliation to vaccine refusal rates, MMR vaccination rates, and MMR vaccination delays. Despite various data limitations, our finding of the emergence and widening of partisan gaps over time suggests that political identity has become an increasingly important factor in childhood health decision-making. Funding: This research was supported in part by the Stanford Institute for Human-Centered Artificial Intelligence and the Robert Wood Johnson Foundation.