The United States is experiencing its worst measles outbreak since the disease was declared eliminated in 2000, with confirmed cases reaching 1,912 as of December 9, 2025, the highest annual total in more than three decades. 

There have been 47 outbreaks reported in 2025, and 88% of confirmed cases (1,673 of 1,912) are outbreak-associated. For comparison, 16 outbreaks were reported during 2024 and 69% of cases (198 of 285) were outbreak-associated.

The outbreak has already claimed three lives this year and resulted in 218 hospitalizations, with 92% of cases occurring among individuals who were unvaccinated or had unknown vaccination status. Public health officials warn that if transmission chains continue into January 2026, the United States risks losing its measles elimination status—a designation the country achieved 25 years ago through sustained high vaccination coverage.

The 2025 measles outbreak began in January in communities with low vaccination coverage along the Texas-New Mexico border. By mid-April, 800 cases had been reported across 25 jurisdictions, a 180% increase over the 285 cases reported during all of 2024. The West Texas outbreak alone accounted for 654 cases across three states—Texas, New Mexico, and Oklahoma—with two unvaccinated school-aged children in Texas dying from the disease, the first measles deaths in the United States in a decade.​ The outbreak predominantly affected children, with 31% of cases in children under age five and 38% in those aged 5-19 years.​

As the year progressed, new outbreaks emerged in Utah, Arizona, and South Carolina. By mid-December, a rapidly spreading outbreak in communities along the Utah-Arizona border had reached 275 cases. South Carolina reported 111 cases since October, with over 250 individuals quarantined due to exposure and 105 patients who had never received a single dose of measles vaccine.​

The outbreaks have been concentrated in areas where kindergarten vaccination rates have fallen below the 95% threshold needed to maintain herd immunity. Gaines County, Texas, the epicenter of the initial outbreak, had vaccination coverage below 82%. Other affected Texas counties showed similarly low rates: Briscoe County at 80%, Childress County at 70.5%, and Dawson County at 88.1%.

Before the introduction of the measles vaccine, the disease was nearly universal among American children, causing an estimated 400-500 deaths, 48,000 hospitalizations, and 1,000 cases of encephalitis (brain swelling) annually in the United States. During the 1950s, an annual average of more than 500,000 measles cases and nearly 500 deaths were reported, though the actual number of cases likely approached 3.5 million per year since virtually all children contracted the disease.

The first measles vaccine was licensed in the United States in 1963, and approximately 15 million children received one of the new measles vaccines between 1963 and mid-1966, causing reported disease incidence to fall by half. In 1968, an improved and more attenuated vaccine developed by Dr. Maurice Hilleman, called the Edmonston-Enders strain, was introduced and has been the only measles vaccine used in the United States since then.​

In 1971, Hilleman combined the measles vaccine with newly developed vaccines for mumps and rubella, creating the MMR (measles, mumps, and rubella) vaccine administered as a single shot. Following a 1989 measles outbreak among vaccinated school-aged children, health authorities recommended adding a second dose of MMR vaccine for all children, which led to even greater declines in reported cases.​

Despite initial predictions in 1967 that measles could be eradicated from the United States within months, fluctuating federal funding for immunization programs through the 1970s and 1980s prevented rapid elimination. However, sustained high vaccination coverage eventually achieved the goal: measles was officially declared eliminated from the United States in March 2000, verified through extensive CDC and expert panel review of epidemiological data and vaccination programs.

The MMR vaccine is highly effective at preventing measles infection. Clinical studies demonstrate that a single dose of MMR vaccine is 93% effective against measles, while two doses provide 97% protection. The vaccine generates long-lasting, typically lifelong immunity against measles.​

To maintain population-level protection and establish herd immunity sufficient to block measles transmission, at least 95% of the population must be immune through vaccination or prior infection. This high threshold is necessary because measles is extraordinarily contagious—approximately 90% of susceptible individuals who are exposed to the virus will become infected.​

The measles virus spreads through respiratory droplets and airborne transmission when an infected person coughs, sneezes, or breathes. The virus can remain airborne or on surfaces for up to two hours. This transmissibility makes measles one of the most contagious diseases known to humans.​

Measles is far from the benign childhood illness some vaccine skeptics claim. The disease causes serious health complications, especially in children younger than five years of age. Common complications include ear infections and diarrhea, while more severe outcomes include pneumonia and encephalitis (brain inflammation).​

Approximately one out of every 1,000 measles patients will develop acute encephalitis, which often results in permanent brain damage. Among those who develop measles encephalitis, mortality rates range from 10-15%, with an additional 25% experiencing permanent neurodevelopmental consequences.​

Death occurs in approximately one to three out of every 1,000 children infected with measles, typically from respiratory and neurologic complications. Measles pneumonia—either viral or from superimposed bacterial infection—is the most common cause of measles deaths. During the 2025 outbreak, the hospitalization rate has been 11%, with 218 people requiring hospital care and three confirmed deaths.​

For pregnant women who contract measles, the disease can cause premature birth or result in low-birth-weight babies. A rare but fatal complication called subacute sclerosing panencephalitis (SSPE)—a degenerative disease of the central nervous system characterized by behavioral and intellectual deterioration and seizures—can develop seven to ten years after measles infection.

Before the vaccine’s introduction, measles caused up to 500 deaths annually in the United States.

The 2025 measles crisis has been fueled by a steady decline in childhood vaccination coverage that began during the COVID-19 pandemic and has continued unabated. National kindergarten coverage with two doses of MMR vaccine fell from 95.2% during the 2019-2020 school year to 92.7% in 2023-2024 and further declined to 92.5% for the 2024-2025 school year—leaving an estimated 280,000 to 286,000 kindergarteners unvaccinated and unprotected against measles.​

Over three-quarters of states (39 out of 50) reported MMR vaccination rates below the 95% threshold during the 2024-2025 school year, up from 28 states during the pre-pandemic 2019-2020 school year. Sixteen states now have vaccination rates below 90%, compared to only three states before the pandemic. Coverage rates vary dramatically by state, ranging from a low of 78.5% in Idaho to a high of 98.2% in Connecticut.​

Exemptions from school vaccination requirements have surged to record levels. The share of kindergarten children claiming an exemption from one or more vaccines increased from 2.5% in 2019-2020 to 3.6% in 2024-2025. By the 2024-2025 school year, 17 states had vaccine exemption rates exceeding 5%, making it mathematically impossible for those states to achieve 95% vaccination coverage even if all non-exempt children were vaccinated.​

Vaccine hesitancy—fueled by misinformation about vaccine safety, distrust of health authorities, and the influence of anti-vaccine activists on social media—has been identified as a primary driver of declining immunization rates. The debunked claim linking the MMR vaccine to autism, originally propagated by a fraudulent 1998 study, remains a leading reason cited by parents who refuse vaccination for their children despite overwhelming scientific consensus on the vaccine’s safety and efficacy.​

The appointment of Robert F. Kennedy Jr., a known promoter of vaccine misinformation, as Secretary of Health and Human Services following President Trump’s second inauguration has further complicated public health efforts. Kennedy initially downplayed the 2025 outbreak, describing it as “not unusual,” and has suggested in interviews that the measles vaccine had harmed children in West Texas and that measles vaccine injuries are more common than known—claims contradicted by extensive research. His past efforts related to vaccine skepticism, including actively promoting vaccine hesitancy during the 2019 Samoa measles outbreak that led to 83 deaths, have raised concerns among public health officials.