How Unique is the Recent Measles Outbreak?

March 18, 2025

Robin Oliverio, Ph.D.

A Look at Measles Trends Nationwide and How Allegheny County Compares

In 2000, the Centers for Disease Control and Prevention declared the measles virus eliminated in the United States , meaning that there were no cases spread over the course of a year. But in 2014, a notable outbreak occurred among visitors at Disneyland. Now, in 2025, a measles outbreak that started in Texas has led to the death of two people .

How has measles managed to reappear after more than a decade? The answers lie in the direct correlation between reduced vaccination rates and the uptick in outbreaks.

History Repeats Itself

The measles vaccine – typically administered in two doses as part of the measles, mumps, and rubella (MMR) vaccine – is the only effective way to prevent infection. Thanks to widespread vaccination efforts, measles cases in the United States dropped significantly beginning in the 1960s, turning a serious childhood disease into a rarity.

In Dec. 2014, an unvaccinated child was hospitalized with the virus after visiting Disneyland, where it quickly spread and infected 147 people . This outbreak impacted some of the most vulnerable groups as children who were still too young or medically unable to be vaccinated became infected . The scope of this outbreak was later linked to under-vaccination .

In 2015, a separate outbreak led to the death of a person with a compromised immune system , the first U.S. measles-related death in 12 years. A nationwide conversation about the importance of vaccinations began again.

By 2019, another outbreak started in New York City after an unvaccinated child carried the virus after traveling internationally. This child’s community had seen a reduction in vaccinations after the neighborhood had received an influx of misinformation related to the vaccine . Of the 649 individuals who were diagnosed and had a known vaccination status, 85.8% were unvaccinated and mostly under the age of 18 .

In 2024 , another outbreak in Chicago resulted in 57 cases over the course of four months . Widespread efforts to provide vaccinations in the affected area were able to prevent the outbreak from growing more significantly .

Recently, an outbreak in Texas – which has subsequently spread to multiple states – began in late Jan. 2025 after two unvaccinated adults contracted the measles virus while traveling internationally and brought it home to a community where 18% of residents had vaccine exemptions . This most recent outbreak has led to the death of two people , one of whom was a six-year-old child, and has infected over 220 individuals . The conversation about the importance of vaccination continues.

The Decline of Vaccination Rates

One of the biggest factors behind these outbreaks? Fewer people are getting vaccinated.The response to the COVID-19 vaccine appears to have an effect of reducing vaccinations

for other diseases.Nationally, the vaccination rate among kindergarteners has dipped to 92.7%

, below the 95% threshold needed to maintain herd immunity

and prevent measles from spreading.

Here in Allegheny County, 94.7% of kindergarteners have received the MMR vaccine

. While kindergarteners in public schools throughout the county have an MMR vaccination rate of 95.4%, the rate among those in religious/parochial schools is 89.5%

We mentioned in a previous article how vaccination is important to establish and maintain herd immunity

, a concept we will elaborate on in an upcoming article.While vaccination may be a personal choice, the effects of that choice go beyond the individual. Those who can’t get vaccinated for medical reasons – such as infants and people with a compromised immune system – rely on community immunity to stay safe. As vaccination rates continue to decline, that protection weakens, and outbreaks are likely to become more frequent.The best way to prevent measles from becoming a routine threat again is to maintain high vaccination rates across the entire population.

To learn more about how to protect your health and the health of your community, talk to your physician or contact the Allegheny County Health Department

About Robin Oliverio, Ph.D.

Robin holds a Ph.D. in neuroscience and is passionate about bridging the gap between science and policy. She focuses on using research to inform evidence-based policies that drive positive societal change. She is strongly committed to projects that make a meaningful difference in people’s lives, and she thrives in roles where science meets advocacy, communication, and impact.

If you have any questions or would like a particular topic to be featured, please reach out to Dr. Oliverio, science communications & media specialist, at OliverioR@CarnegieScienceCenter.org