The United States has recorded over 2,000 measles cases for the first time in 33 years. Concurrently, a new study indicates that children who miss early childhood vaccinations are more likely to not receive the measles, mumps, rubella (MMR) vaccine by age two. This research emerges amidst a decline in MMR vaccination rates observed in recent years.
Study Overview
Published in JAMA Network Open, the study analyzed data from Truevata, an electronic health records database encompassing multiple U.S. healthcare systems. The participant group included over 321,000 children who received routine care from January 1, 2018, to April 30, 2025, covering their first two months, first year, and second year of life.
Vaccination Guidelines and Findings
The Centers for Disease Control and Prevention (CDC) recommends two doses of the MMR vaccine: the first between 12 and 15 months of age, and the second between 4 and 6 years. One dose provides 93% effectiveness against measles, while two doses offer 97% effectiveness.
Key findings from the study include:
- 78.4% of children received the MMR vaccine on schedule.
- 13.9% experienced delayed vaccination.
- 1% received the MMR vaccine early.
- 6.7% did not receive the MMR vaccine by age two.
The strongest indicators for not receiving the MMR vaccine were delays in the recommended 2-month and 4-month vaccinations. These earlier vaccines include diphtheria, tetanus, and acellular pertussis (DTaP); Haemophilus influenzae type b (Hib); pneumococcal conjugate vaccine (PCV); and inactivated poliovirus vaccines (IPV).
Children who received their 2-month vaccines on time were seven times more likely to receive the MMR vaccine.
Trends in Vaccination Rates
The percentage of children receiving the MMR vaccine on time fluctuated during the study period:
- 75.6% in 2018.
- Increased to 79.9% in 2021.
- Decreased to 76.9% in 2024.
This decline between 2021 and 2024 corresponded with an increase in the percentage of children who had not received the MMR vaccine by age two, rising from 5.3% in 2020 to 7.7% in 2024.
Demographic Factors
The study identified specific groups more likely to be unvaccinated for the MMR shot by age two:
- Boys.
- Children identified as white and non-Hispanic or Latino.
- Rural residency was associated with a slight increase in the risk of no MMR vaccination, even among children with consistent access to care.
Public Health Implications
Study authors noted that these results suggest potential increases in vaccine hesitancy or unmeasured challenges related to access to care. The findings highlight the importance of early intervention to encourage timely childhood vaccinations.
Dr. Amesh Adalja of Johns Hopkins Center for Health Security, who was not involved in the study, commented on the public health significance, stating that increased vaccination is essential for maintaining measles elimination status and reducing the impact of infectious diseases within communities.