Evaluating recent trends in early measles vaccinations in Texas

• Among children in Texas receiving a first measles vaccine prior to two years of life:
  • In March and April 2025, 20.1% of all first measles vaccines were administered to children early (6-11 months). This is 11.5-fold higher than in 2019, when there were international and domestic outbreaks.
  • In 2025, 4.3% of all first measles vaccines were administered to children who were six months old; 8.5-fold higher than in 2019.
• In April 2025, 10.0% of 10-month-old children in Texas had received at least one measles vaccine; this is 10.4-fold higher than the January 2024-January 2025 average. In April 2025, 8.7% of six-month-olds in Texas received a measles vaccine; this is 31.7-fold increase compared to the January 2024 – January 2025 average (0.3%).

Measles is one of the most contagious diseases in the world (1, 2). It spreads through the air when an infected person coughs or sneezes, and it can linger in the air for up to two hours (1). Fortunately, the measles vaccine (administered in the US as the combined measles, mumps, rubella vaccine, MMR or MMRV) is highly effective – with 93% effectiveness after one dose and 97% effectiveness after two doses (3). However, when vaccination rates drop, outbreaks can occur among susceptible populations, primarily children.

We’ve recently released two reports looking at measles vaccination trends for children getting the first and second dose on time across the US. The CDC recommends the first vaccine between 12-15 months; however, our results showed a stark decline in the number of kids receiving the vaccine on-time from 2020 to 2024. The CDC also recommends an early, or ‘zero’ dose of the MMR vaccine for infants 6-11 months old before international travel (3). This dose does not replace the first dose in the series, with children who receive this early dose requiring the routine series after their early dose of the vaccine.

Thus far in 2025, the US has reported 1,024 measles cases, more than triple the number of cases in 2024, and the second highest annual case total since endemic spread of measles ended in the US in 2000, second only to 2019 (4). The majority (70+%) of these cases are in the state of Texas, where a large outbreak is spreading among a close-knit, under-vaccinated community (5). In response to elevated case totals this year and the large, continuing outbreak in Texas, the CDC updated its measles vaccination guidelines to advise children who live in or travel to counties with active outbreaks to receive an early measles vaccination (6, 7). The weekly reported number of measles cases has been slowing slightly in recent weeks, and we aimed to understand whether recent changes in vaccine guidelines may be contributing.

In this report, we aimed to understand whether children in Texas are receiving an early dose of the measles vaccine and quantified changes in age-related vaccination patterns.

Methods

Using a subset of Truveta Data, this analysis included patients who had an outpatient encounter between 2-3 months, 4-5 months, and 6 -11 months of life and who resided in Texas.

We identified children who received a measles vaccine (MMR or MMRV) and the age at which they received their first vaccine. Vaccination events recorded prior to age 6 months (182 days) were assumed to be erroneous and excluded (8). Measles vaccines received at 24 months or later were excluded from this analysis.

Among children with a measles vaccine, percent with an early administration

Within each calendar month, we calculated the proportion of measles vaccinations that were administered early (between 6 – 11 months of age). We also classified the age (in months) at which the vaccine was administered. We show yearly trends of the percent of vaccines that were administered for each early age group (6 months, 7 months, etc.) from January 2019 through April 2025.

Percentage of children vaccinated by age group

We calculated the percentage of children who had received one measles vaccine by each age group over time. For each calendar month, we identified the number of children in each age group (6–11 months) and calculated the proportion who had received at least one measles vaccine during that month or earlier. For example, for each month, we show the percentage of children who had been vaccinated by age six months, seven months, eight months, and so on. We plot these proportions from January 2024 to April 2025, grouping children by their age in months.

Results

Within this study, 82,949 children with routine outpatient encounters in Texas were included; 80.5% had evidence of at least one measles vaccine dose prior to 2 years of age.

Among children with a measles vaccine, percent with an early administration

Among children receiving a first measles vaccine between 6 months and 23 months of age, we observe a sharp increase in the proportion of vaccines administered early starting in February 2025; in March and April 20.1% of all first measles vaccines received by 23 months of age were administered early (to 6–11-month-olds). From 2020 through January 2025, the proportion of first measles vaccinations administered early in Texas was steady and low at (0.7%). The proportion of children receiving early vaccination in 2019 was elevated (1.7%), corresponding to large measles outbreaks domestically and internationally in 2019 that prompted a similar recommendation for early measles vaccination; however, the spike in March and April 2025 is 11.5-fold higher than 2019.

Most children who received the vaccine early in 2025 received it at six months of age – 4.3% of all measles vaccines given prior to 2 years were given at six months.

In 2019, 0.5% of vaccines were given at six months, and between 2020 and 2024, the average was 0.1%. That means in 2025, the percent of vaccines administered at six months of age is 8.5-fold higher than the 2019 rate, the second highest year in our analysis and the year with the most measles cases since 2000.

Vaccine administration rates were also high amongst children in the 9-month age group – 3.9% of all measles vaccines given prior to 2 years were given at nine months. This was 7.5-fold higher than the 2019 rate of 0.5%.

Percentage of children vaccinated by age group

From January 2024 to January 2025, the measles vaccination rate for all age groups was under 2%.

In April 2025, the vaccination rate was highest for 10-month-olds at 10.0%. This is 10.4-fold higher than the January 2024 – January 2025 average.

Vaccination rates were also high for six-month-olds at 8.7%, a 31.7-fold increase compared to the January 2024 – January 2025 average (0.3%).

11-month and 8-month-olds had the lowest rates, likely due to the timing of the recommendation changes (March 2025), meaning that these children had not yet had a pediatric well child visit (routine visits recommended at 6-, 9-, and 12-months).

Discussion

Since late January 2025, there have been 718 cases of measles reported in Texas and two deaths among unvaccinated children (5). This outbreak represents the single largest measles outbreak in the US since elimination was declared in 2000 (although 2019 had more cases, there were two large outbreaks that year) (9). Because the first measles vaccination is recommended routinely at 12-15 months of age, parents of young children are typically required to wait a year to get protection for their children against the measles virus. Maternal antibodies provide some protection for very young infants against measles (10), but measles can be very serious, especially for young children, and having to wait to vaccinate a child can cause anxiety for parents (11). Ordinarily, measles transmission in the US is rare given its elimination status, and thus measles risk is very low for infants, however the current outbreak paints a different picture. With CDC’s updated recommendation for a 6–11-month dose for those in or traveling to outbreak areas, parents can now vaccinate their children early and know that their children are protected (12).

Our data show that starting in February 2025 and accelerating in March and April with the issuance of CDC’s Health Alert Network (HAN) about measles transmission on March 7, 2025, Texas parents are taking advantage of the early vaccine recommendation (7). These results highlight that the outbreak is causing real concern for parents and changing vaccination behavior. Routine well child visits typically occur at 6- and 9-months. Our results show that children who had a 6- or 9- month visit during March or April 2025 received higher rates of vaccination than children who will have their next regular visit in May 2025 (i.e., 8- and 11-month-olds). However, the results presented here do show an increase in measles vaccination rates for 8- and 11-month-olds, which may indicate that some parents are bringing their children to their pediatrician for an extra visit to get them vaccinated early.

This study has a few limitations. First, the analysis is based on unadjusted rates and does not account for demographic or socioeconomic factors that may influence vaccination uptake in Texas. Second, measles vaccination records rely on electronic health data, which may be incomplete if a child’s vaccination occurred outside of a constituent Truveta healthcare system Finally, we required children to have regular care interactions with the health system. Children without regular visits at 2-3 months, 4-5 months, and 6-11 months were not included in this analysis, which likely means these vaccination rates are slightly higher than the overall population of children in Texas who may have less healthcare-seeking behavior.

Measles outbreaks typically spread within communities with low vaccination rates, where many individuals are susceptible to the disease. Without stringent control measures, outbreaks usually subside only when the virus can no longer spread to new individuals (13). This reduction in susceptibility can occur through targeted public health interventions like mass vaccination campaigns, or an outbreak running its course, and infecting the majority of the population at risk. In recent weeks, the Texas outbreak has seemed to slow slightly (14), and these data may give us an optimistic reason why: perhaps increasing vaccination among children normally too young to be vaccinated is reducing the susceptible population.

These are preliminary research findings and not peer reviewed. Data are constantly changing and updating. These findings are consistent with data accessed on May 12, 2025.

Citations

1. Centers for Disease Control and Prevention, About Measles, Measles (Rubeola) (2024). https://www.cdc.gov/measles/about/index.html.
2. Centers for Disease Control and Prevention, Measles Symptoms and Complications, Measles (Rubeola) (2024). https://www.cdc.gov/measles/signs-symptoms/index.html.
3. Centers for Disease Control and Prevention, Measles Vaccination, Measles (Rubeola) (2025). https://www.cdc.gov/measles/vaccines/index.html.
4. Centers for Disease Control and Prevention, Measles Cases and Outbreaks, Measles (Rubeola) (2025). https://www.cdc.gov/measles/data-research/index.html.
5. Texas Health and Human Services, Measles Outbreak – May 16, 2025 (2025). https://www.dshs.texas.gov/news-alerts/measles-outbreak-2025.
6. Texas Department of State Health Services, “DSHS measles outbreak vaccination recommendations for children who live in or visit counties with ongoing measles transmission” (2025); https://www.dshs.texas.gov/sites/default/files/Admin-Meales/doc/measles-vaccination-pep-recommendations.pdf.
7. Centers for Disease Control and Prevention, “Expanding Measles Outbreak in the United States and Guidance for the Upcoming Travel Season” (2025).
8. Centers for Disease Control and Prevention, Routine Measles, Mumps, and Rubella Vaccination, Vaccines & Immunizations (2021). https://www.cdc.gov/vaccines/vpd/mmr/hcp/recommendations.html.
9. S. Simpson, Texas’ measles outbreak is nation’s largest since 2000, The Texas Tribune (2025). https://www.texastribune.org/2025/05/08/texas-measles-spread-oklahoma-new-mexico/.
10. E. Leuridan, P. Van Damme, Passive transmission and persistence of naturally acquired or vaccine-induced maternal antibodies against measles in newborns. Vaccine 25, 6296–6304 (2007).
11. A. Henson, I Got My Baby Vaccinated for Measles Early Because I Live in Texas Where 2 Children Have Died (Exclusive) (2025). https://people.com/measles-texas-vaccinated-early-mom-shares-story-exclusive-11712397.
12. A. Tin, Extra measles vaccine shot recommended for some travelers to Texas, other areas with outbreaks, CDC says (2025). https://www.cbsnews.com/news/measles-vaccine-cdc-texas-kansas-travel/.
13. N. B. Masters, M. C. Eisenberg, P. L. Delamater, M. Kay, M. L. Boulton, J. Zelner, Fine-scale spatial clustering of measles nonvaccination that increases outbreak potential is obscured by aggregated reporting data. Proc. Natl. Acad. Sci. U.S.A. 117, 28506–28514 (2020).
14. J. Sonnenmair, As measles outbreak slows in West Texas, doctors remain on alert (2025).