TOPLINE: 

Among children with regular healthcare access, delayed 2- and 4-month vaccinations were associated with markedly higher odds of missing measles, mumps, and rubella (MMR) vaccination by the age of 2 years.

METHODOLOGY:

• Researchers conducted a retrospective cohort study to characterize coverage and trends of timely MMR vaccination and identify factors associated with late vaccination and nonvaccination by the age of 2 years in 321,743 children (51.6% boys) who received regular care in the US.
• Vaccine doses recorded from birth through 24 months were included; vaccination outcomes were assessed from January 2018 to April 2025.
• For the 2- and 4-month vaccine series, a child's vaccination was classified as on time if all vaccines in the series were administered within CDC-recommended age ranges and dosing intervals (at the current time) and late if all vaccines were either late or not administered.
• The primary outcome was the MMR vaccination status by the age of 2 years: on time (12-15 months), late (16-23 months), or not administered; children were followed up from birth until 24 months of age.
• Analyses were stratified according to the timing of the COVID pandemic.

TAKEAWAY:

• Timely MMR coverage declined from 79.9% in 2021 to 76.9% in 2024, whereas the proportion of children with no MMR vaccination by the age of 2 years increased from 5.3% in 2020 to 7.7% in 2024.
• In the post-COVID period, children who were late on 2-month vaccines had nearly sevenfold higher odds of no MMR vaccination by the age of 2 years (adjusted odds ratio [aOR], 6.96; 95% CI, 6.60-7.34); being late on 4-month vaccines also increased the odds (aOR, 6.16; 95% CI, 5.84-6.50).
• Factors associated with higher odds of nonvaccination included male sex (aOR, 1.12), rural residence (aOR, 1.09), White race (aOR, 1.48), and non-Hispanic or Latino ethnicity (aOR, 1.51).
• In analyses of late vs on-time MMR vaccination, children who adhered to the American Academy of Pediatrics well-child visit schedule in the first 2 years were substantially more likely to receive MMR on time.

IN PRACTICE:

"This study of children with regular access to care shows that childhood vaccine coverage and timeliness have been decreasing since the COVID-19 pandemic and that staying on the vaccine schedule early is the factor most associated with receiving a timely MMR vaccine, the best protection against the measles outbreaks that are spreading rapidly across the US ," the authors wrote.

SOURCE:

The study was led by Nina B. Masters, PhD, MPH, Truveta Research, Truveta Inc, Bellevue, Washington. It was published online on January 02, 2026, in JAMA Network Open.

LIMITATIONS: 

Given that the study population received regular care over 2 years, the findings may not be applicable to all US children and likely reflect higher healthcare use and vaccination rates than the general population. Vaccinations administered outside participating Truveta constituent health systems were not captured. Moreover, the data came from a limited number of US states.

DISCLOSURES:

The study was funded by Truveta Inc. All six authors reported being employed by Truveta, and several disclosed holding equity or stock/stock options in the company.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.