Delayed early vaccines strongly predict missed MMR shots, contributing to rising measles cases and declining U.S. vaccination rates.

Children who miss early vaccines are far more likely to miss the MMR shot by age 2, a study of over 321,000 U.S. children found. Delayed or missed 2- and 4-month vaccines were strong predictors of MMR delays, with on-time early shots increasing MMR likelihood sevenfold. Only 78.4% received MMR on time, down from 79.9% in 2021, while unvaccinated children rose to 7.7% by 2024. Boys, white and non-Hispanic or Latino children, and those in rural areas were more likely to be unvaccinated. The U.S. saw over 2,000 measles cases in 2025—the highest in over 30 years—raising public health concerns as vaccination rates decline. Experts stress early pediatrician engagement to build trust and combat hesitancy.