Credit: Julio Cortez/Associated Press, File
A sign is seen outside of Seminole Hospital District offering measles testing on February 21, 2025, in Seminole, Texas. Officials in Gaines County have established vaccine clinics for parents and children to provide the MMR shot.
The growing measles outbreak that has sickened at least 198 people and led to 1 child’s death is happening in one of Texas’s least vaccinated counties.
Only 82 percent of children in Gaines County are up-to-date on their measles-mumps-rubella (MMR) vaccines, according to state health records, compared to 94.3 percent statewide. That’s likely an overestimate, experts say, since it doesn’t include children who are homeschooled or attend private schools. New Mexico's Lea County, which is adjacent to Gaines County, has also reported 30 cases, according to the New Mexico Department of Health.
Before American scientist John Enders and colleagues developed the measles vaccine in 1963, the virus was a common childhood infection in the US. Caused by a morbillivirus, measles spreads rapidly and causes symptoms such as fever, rash, sore throat, and bronchitis. While the condition can be relatively mild, 1 in 5 of those infected will require hospitalization, and 1 in 20 develop pneumonia. A smaller proportion can develop brain swelling known as encephalitis. Approximately 1 to 3 out of every 1,000 children infected with measles will die, according to the US Centers for Disease Control and Prevention.
“It is the most contagious infectious disease I know of in humans,” says Robert Bednarczyk, an epidemiologist at the Rollins School of Public Health at Emory University in Atlanta.
After being eliminated from the US in 2000, measles has rebounded due to declining childhood vaccination rates around the country. The CDC estimates that 92.7 percent of US kindergarteners received both doses of the MMR vaccine for the 2023–2024 school year. That’s lower than in 2019, when 95.2 percent of kindergarteners were up-to-date.
Nearly all cases in the Texas outbreak have occurred among unvaccinated children, with five infections among those who were already immunized—a rare occurrence.
“Because the vaccine contains live, attenuated viruses, it gives the same immunity as having a natural infection. And people who have had natural measles don't get reinfected,” says Stanley Plotkin, emeritus professor of pediatrics at the University of Pennsylvania.
Protecting your neighbors
Administered in two doses, the MMR vaccine uses a weakened, lab-grown measles virus to provoke lifelong immunity. The widespread uptake of this vaccine caused measles cases in the US to plummet by over 99 percent between 1962 and 1980. After less than 50 years, measles had essentially disappeared in the US—a ringing public health success.
Yet hesitancy about vaccines began to grow after a fraudulent paper linking the MMR vaccine to autism was published in 1997 in The Lancet. More recently, online echo chambers have enabled vaccine myths and misinformation to thrive on social media. The COVID-19 pandemic also affected routine childhood immunizations by making it more challenging to attend physicians’ offices and clinics.
Overall, the Texas outbreak highlights the importance of promoting routine childhood immunization, says Amesh Adalja, an infectious disease physician and senior scholar at the Johns Hopkins Center for Health Security in Baltimore.
For one, measles can harm a child’s health even after the infection has cleared. The virus can cause a phenomenon called immune amnesia, which destroys large numbers of beneficial B and T cells. Immune amnesia can occur in 11 to 73 percent of measles cases, according to a 2019Science paper. From several months to several years after an infection, even a mild one, a person is much more vulnerable to acquiring other infectious diseases.
What’s more, getting vaccinated protects the community. The CDC’s Advisory Committee on Immunization Practices recommends two doses of the MMR vaccine for individuals to ensure adequate measles immunity in their community. Because the virus is so contagious, 95 percent of individuals need to be immune to the virus via vaccination to prevent an outbreak.
Credit: Getty Images
A staff member administers a dose of the measles vaccine to a child at a health center in Lubbock, Texas, on February 27, 2025.
Making breakthrough infections even rarer
Breakthrough infections in vaccinated populations aren’t well understood, but they could stem from a person’s individual genes, which make their bodies less able to recognize and combat the measles virus.
Adalja also points out that some of the five breakthrough infections in Texas may have occurred in recently vaccinated people who got measles before their immune systems had fully responded to the vaccine.
High MMR coverage will make infections, breakthrough or otherwise, even rarer than they already are. To that end, officials in Gaines County have established vaccine clinics for parents and children to provide the MMR shot.
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“Those that are vaccine hesitant sometimes need a reminder that measles is an important disease,” Adalja says. “This is an impetus for many people to reconsider some of their false assumptions about measles.”