Early MMR Vaccine Adoption During the 2025 Texas Measles Outbreak

Abstract

This cross-sectional study examines early vaccination rates for measles in Texas following updated 2025 guidance from the US Centers for Disease Control and Prevention.

Introduction

As of August 5, 2025, the US has reported 1356 measles cases, the largest number of cases since elimination was declared in 2000.¹ Most of these cases have occurred in Texas.² In response to the growing Texas outbreak, the US Centers for Disease Control and Prevention (CDC) issued updated guidelines through the Health Alert Network (HAN) on March 7, 2025, recommending early vaccination (ages 6 to 11 months) for children living in or traveling to affected counties.³ This analysis examined whether children in Texas received early measles vaccination following the HAN and assessed shifts in age-related vaccination patterns.

Methods

We identified infants residing in Texas within Truveta Data who had outpatient encounters at 2 to 4, 4 to 6, and 6 to 11 months of age between 2019 and April 2025 (henceforth referred to as regular care). Truveta Data consists of electronic health records provided by member US health care systems that have been deidentified by expert determination in accordance with the HIPAA Privacy Rule.⁴ Because analysis involved only deidentified data and contained no identifiable private information, the study did not constitute human participants research as defined by the US Department of Health and Human Services (45 CFR 46) and therefore did not require institutional review board approval.

We identified MMR or MMRV vaccines administered between 182 days and 24 months of age. We then conducted 2 analyses. First, for each calendar month, we calculated the proportion of measles vaccinations administered early (between 6 to 11 months of age) among children with regular care. Second, we calculated the proportion of children with regular care who were vaccinated, by age in months (6 to 11 months) from January 2024 to April 2025. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline was followed when conducting this study.

Results

This study included 82 949 children in Texas receiving regular care (40 322 female [48.6%]; 25 085 Hispanic or Latino ethnicity [30.2%]; 3591 Asian [4.3%], 10 379 Black [12.5%], 52 961 White [63.8%] race); 66 749 children (80.5%) received at least 1 measles vaccine before age 2 years. Among children who received their first measles vaccine by 24 months of age, we observed a sharp rise in the proportion receiving early vaccination (ages 6 to 11 months) beginning in February 2025 (Figure 1). In March and April, 422 of 2094 first doses (20.1%) were given early. The proportion of early vaccination remained at 0.7% (332 early doses of 48 453 total) from 2020 through January 2025. During 2019, the proportion of children receiving early vaccination was also higher (153 of 8781 doses [1.7%]), when a different outbreak prompted similar recommendations, but the March-April 2025 rate was 11.5-fold higher.

Figure 1. Proportion of Vaccines Administered Early (Ages 6 to 11 Months) Among Children Who Received a Measles Vaccine Prior to Age 2 Years.

From January 2024 to January 2025 (baseline, preoutbreak period), monthly vaccination rates for all age groups were below 2% (Figure 2). In April 2025, rates peaked at 10.0% for 10-month-olds (a 10.4-fold increase from baseline). Six-month-olds also had high rates at 8.7%; a 31.7-fold increase from baseline (0.3%). In April 2025, vaccination rates were lowest among children ages 11 and 8 months.

Figure 2. Monthly Percentage of Children Who Received a Measles Vaccine by Age Group.

Discussion

In concordance with CDC recommendations, our data show a rapid rise in early measles vaccination in early 2025. These data suggest an increase in early vaccination started in February, even before the updated guidelines were issued, potentially due to clinician and/or parental concern.

Routine well-child visits occur at ages 6 and 9 months.⁵ Children with well-child visits in March or April 2025 had higher vaccination rates than those due for visits in May (eg, 8- and 11-month-olds), suggesting that pediatric well-child visits are an opportunity for early vaccination in Texas. Still, increased rates among 8- and 11-month-olds suggest non–regular care visits may have contributed to early vaccination. Other outreach strategies, such as reminder recall, could be used to further increase vaccination rates⁶.

Our cross-sectional study had limitations. First, it reported unadjusted rates and did not account for factors affecting vaccine uptake. Second, vaccination records outside of the US health system in the Truveta database were not included. Third, by including only children with regular health care interactions, our estimates likely overrepresented vaccination rates in the broader Texas population.

The Texas outbreak began to slow in May 2025, and as of August 13, 2025, 2 incubation periods have passed since the last reported case in Texas.² These data suggest that increased vaccination among younger children may have helped reduce the risk of cases among those at greatest risk.

Supplement.

Data Sharing Statement