Vaccination has been one of the greatest public health achievements of the last century, drastically reducing childhood morbidity and mortality worldwide. Among the vaccines, the measles, mumps, and rubella (MMR) vaccine is critical due to the high contagiousness of measles and the severe complications it can cause. Recent research indicates a worrying decline in timely MMR vaccination among children in the United States. A cohort study led by Nina B. Masters, PhD, MPH, and colleagues, published in JAMA Network Open, explores changes in MMR vaccination coverage and the factors associated with delayed or missed vaccinations since the COVID-19 pandemic.
The study followed 321,743 children who received regular care within Truveta, a US electronic health record (EHR) database, over the first two years of life. The researchers found that timely MMR vaccination decreased by three percentage points from 2021 to 2024. Specifically, 78.4% of children received their first MMR vaccine on time, 13.9% received it late, and 6.7% had no MMR vaccination recorded by two years of age. Early vaccinations were rare, accounting for only 1% of cases.
The study identified that children who did not receive their routine 2- and 4-month vaccinations on time were significantly more likely not to receive MMR vaccination by age two. Late 2-month vaccines increased the odds of nonvaccination by nearly seven times, while late 4-month vaccines increased the odds by six times. Early adherence to the vaccination schedule is therefore strongly associated with timely MMR vaccination.
Table: First MMR Vaccine Timing by Two Years of Age
| Timing of MMR Vaccine | Number of Children | Percentage |
|---|---|---|
| Early (6-11 months) | 3,106 | 1.0% |
| On Time (12-15 months) | 252,250 | 78.4% |
| Late (16-23 months) | 44,718 | 13.9% |
| No Vaccine Recorded | 21,669 | 6.7% |
Beyond MMR, the study examined other vaccines in the early childhood primary series, including DTaP, Hib, polio, rotavirus, and PCV vaccines. Timely completion of these 2- and 4-month vaccines decreased after the COVID-19 pandemic. For example, on-time DTaP coverage dropped from 86.5% in 2019 to 84.3% in 2023 for the first dose, and from 84.5% to 82.2% for the second dose. These trends indicate a broader decline in adherence to recommended vaccination schedules, which could increase vulnerability to multiple vaccine-preventable diseases.
The COVID-19 pandemic influenced vaccine behavior in multiple ways. The study suggests a spillover effect, where hesitancy or delays surrounding COVID-19 vaccines may have increased hesitancy toward other routine childhood vaccines. Post-pandemic data showed that children eligible for MMR vaccination in 2024 had 1.35 times the odds of nonvaccination compared to children in 2020. This trend coincides with a rise in measles cases in the United States, reaching the highest levels since 2000, including the first measles deaths in a decade.
Sociodemographic Factors
The study examined associations between vaccination outcomes and demographic variables. Male children were slightly more likely to be unvaccinated. Children living in rural areas or in areas of unknown urbanicity also had higher odds of missing MMR vaccination. White and non-Hispanic children were more likely to be unvaccinated, suggesting that vaccine hesitancy persists even among families with regular access to healthcare. Conversely, adherence to the American Academy of Pediatrics (AAP) well child visit schedule was associated with lower odds of nonvaccination.
The study also revealed differences between late vaccination and nonvaccination. Late MMR vaccination was strongly associated with late 4-month vaccine receipt, followed by late 2-month vaccines. Children in rural areas and Asian children were more likely to receive timely MMR vaccination once engaged in care, highlighting the nuanced interplay of geographic, demographic, and behavioral factors.
The findings underscore the importance of early intervention. Pediatricians can use initial 2- and 4-month visits as critical opportunities to address vaccine delays. Research shows that a presumptive communication style, in which clinicians frame vaccination as standard practice, significantly improves vaccine uptake. For example, saying, "Your child is getting two shots today" results in higher adherence than asking parents, "Do you want your child to get vaccines today?"
Additionally, integrating vaccination reminders and flags within EHR systems can help clinicians identify children at risk of falling behind. By leveraging timely data, healthcare providers can proactively reach families, reducing delays and preventing nonvaccination.
Vaccine hesitancy remains a complex issue influenced by misinformation, personal beliefs, and historical concerns. The study discusses the lingering impact of a fraudulent 1998 article linking MMR vaccination to autism spectrum disorder. This fear may disproportionately affect parents of male children, as autism is more commonly diagnosed in boys. Addressing vaccine hesitancy requires clear, evidence-based communication and community engagement to rebuild trust in routine immunizations.
Decreasing vaccination timeliness has significant public health consequences. Measles is highly contagious, and declining MMR coverage creates pockets of susceptibility that facilitate outbreaks. Declining timeliness in other early vaccines increases the risk of pertussis, polio, Hib, and rotavirus infections. In 2025, increased infant deaths from pertussis in the US highlight the urgent need for intervention to restore vaccination coverage.
This research offers several strengths. It uses a large, geographically diverse cohort with EHR data spanning multiple healthcare systems, providing timely insights into vaccination trends through April 2025. By including state-level random effects, the study accounts for geographic clustering and variations in vaccine laws. The use of structured EHR data and procedural codes allows for precise identification of vaccination timing and adherence. The two-year follow-up for each child enables analysis of individual vaccination trajectories.
Despite its strengths, the study has limitations. The cohort represents children with consistent healthcare access, potentially overestimating vaccination coverage compared to the general US population. Vaccinations administered outside participating healthcare systems, during travel, or at pharmacies may not be captured. The dataset is not fully representative of all US regions, as it primarily includes states such as Texas, Washington, Wisconsin, Iowa, California, Illinois, Michigan, Louisiana, Oregon, and Hawaii. EHR data may contain minor inaccuracies, though vaccination recording is typically reliable.
Recommendations and Future Directions
The study emphasizes early interventions to maintain vaccination schedules. Healthcare systems can implement automated EHR reminders for missed early vaccines, support pediatricians in using effective communication strategies, and engage in public education campaigns to counter misinformation. Further research should investigate vaccination trends among children without regular healthcare access and assess the broader impact of the COVID-19 pandemic on vaccine adherence.
The recent decline in timely MMR vaccination and other early childhood vaccines is a public health concern with direct implications for measles outbreaks and other preventable diseases. Early adherence to the vaccination schedule, especially 2- and 4-month vaccines, strongly predicts timely MMR vaccination. Pediatricians and healthcare systems have a critical role in identifying at-risk children, providing early interventions, and promoting adherence to recommended vaccine schedules. Leveraging EHR data for real-time monitoring can support targeted efforts to maintain population immunity and protect children from preventable diseases.
By addressing vaccine hesitancy and delays early, particularly during the first year of life, healthcare providers can ensure children receive critical immunizations on time, reducing the risk of outbreaks and safeguarding public health.
Source: Masters NB, Cartwright BMG, Rodriguez PJ, et al. Delayed or Absent First Dose of Measles, Mumps, and Rubella Vaccination. JAMA Netw Open. Published online January 2, 2026;9(1):e2551814. doi:10.1001/jamanetworkopen.2025.51814
Disclaimer: This blog is for informational purposes only and is based on publicly available research. It is not intended as medical advice. Parents and caregivers should consult their child’s healthcare provider regarding vaccinations and immunization schedules.
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