Southwest U.S. Measles Outbreak Reaches 935 Cases: Officials Warn of Herd Immunity Collapse
The 2025 measles outbreak in the southwestern United States has surpassed 935 confirmed cases, resulting in three deaths. Most infections occurred among unvaccinated individuals, highlighting a concerning decline in vaccination rates. Health experts warn that the loss of herd immunity could lead to the endemic reintroduction of the disease in the country.
Measles was considered eradicated in the US in 2000 through achieving herd immunity with vaccination.AP
Southwest U.S. Measles Outbreak Reaches 935 Cases: Officials Warn of Herd Immunity Collapse
The 2025 measles outbreak in the southwestern United States has surpassed 935 confirmed cases, resulting in three deaths. Most infections occurred among unvaccinated individuals, highlighting a concerning decline in vaccination rates. Health experts warn that the loss of herd immunity could lead to the endemic reintroduction of the disease in the country.
Outbreak and location:
In 2025, the United States is facing its largest measles outbreak in over two decades, with 935 confirmed cases and three deaths reported as of early May.
The epicenter is located in West Texas, particularly Gaines County, which alone accounts for 396 cases.
Additional cases have been reported in New Mexico, Oklahoma, and Kansas, with the outbreak also spreading into the Mexican state of Chihuahua — especially in Mennonite communities with low vaccination rates.
Vaccination and causes:
According to the Centers for Disease Control and Prevention (CDC), 96% of those infected were unvaccinated.
The national vaccination rate has dropped to 91%, below the 95% threshold required to maintain herd immunity.
This decline is tied to the rise of the anti-vaccination movement and the widespread dissemination of vaccine misinformation via social media.
Authorities' warnings:
Experts warn that if measles transmission continues for 12 consecutive months, the U.S. could lose its measles elimination status, achieved in 2000.
Dr. Paul Offit from the Children’s Hospital of Philadelphia stated that the world may be entering a “post-herd immunity” era, where measles is the first disease to re-emerge as vaccination coverage drops.
Deaths and hospitalizations:
The outbreak has resulted in three deaths: two unvaccinated children in Texas and one adult in New Mexico.
Approximately 13% of those infected have been hospitalized.
Continental context:
The World Health Organization (WHO) reported more than 2,300 measles cases across the Americas between January and April 2025, including in Brazil — representing an 11-fold increase compared to the same period in 2024.
Recommendations:
Health officials emphasize the importance of the MMR (measles, mumps, rubella) vaccine, which is 97% effective in preventing measles.
Emergency vaccination campaigns are underway in affected regions.
Experts call for urgent action to contain the outbreak and prevent measles from becoming endemic again in the U.S.