The rising number of measles cases around the world is a clear warning sign that outbreaks of other vaccine-preventable diseases could be next, the World Health Organization warned on Friday.
“It is crucial to understand why measles is important,” said Dr Kate O’Brien, director of WHO’s Department of Immunization, Vaccines and Biologicals. “Its high transmissibility means that even small drops in vaccine coverage can trigger outbreaks, like a fire alarm going off when smoke is first detected.”
That is, measles is usually the first disease to appear when vaccination rates generally decline.
“When we see cases of measles, it indicates that there are almost certainly gaps in other vaccine-preventable diseases like diphtheria, whooping cough or polio, although they may not be setting off the fire alarm yet,” O’Brien said at a news conference on Monday, ahead of the publication of WHO’s Progress Towards Eliminating Measles report, published on Friday in its Weekly Epidemiological Record.
In fact, cases of whooping cough are also increasing in the United States and are on track to be the highest in a decade. According to the Centers for Disease Control and Prevention, more than 20,000 cases of whooping cough have been reported so far in 2025.
According to the report, it is estimated that in 2024 there will be 11 million measles infections worldwide, almost 800,000 more than those recorded in 2019.
Last year, 59 countries reported large measles outbreaks. In 2025, the United States joined the list of countries.
Threatened removal status
Current outbreaks threaten some countries’ so-called measles elimination states.
Elimination means that a virus has stopped spreading in a specific country or region. (Only one virus, smallpox, has been eradicated or permanently eliminated worldwide.)
In total, 81 countries had reached elimination status by 2024, according to the WHO. Canada eliminated measles in 1998. Two years later, the United States followed suit.
Elimination status means a country has the ability to stop an outbreak when measles cases arrive from abroad, O’Brien said. If vaccination rates are high enough, the virus won’t have enough unvaccinated people to infect, stopping an outbreak in its tracks.
But vaccination rates in the United States are falling: An NBC News investigation found that since 2019, 77% of counties and jurisdictions have reported declines in the number of children receiving routine childhood vaccines, such as measles, mumps and rubella vaccines.
The key determining factor for a country to lose its measles elimination status is the continued spread of the same strain of the virus for a full year.
Canada met that threshold this month. The United States could be next if scientists can trace current cases to an outbreak in Texas that began in January.
Nearly all of the samples tested from those early cases were identified as a measles genotype called D8, according to a CDC report published in April.
The D8 genotype was recently detected in an outbreak in South Carolina.
Preliminary results from samples sent from South Carolina to CDC labs “are the same type, D8, that is seen in other settings in the United States,” Dr. Linda Bell, state epidemiologist with the South Carolina Department of Public Health, said at a news conference Tuesday.
Additional genetic sequencing is needed to establish a definitive link between the Texas outbreak and the South Carolina outbreak, as well as the Utah and Arizona outbreaks. A spokesperson for the South Carolina Department of Public Health said the agency “expects those results in the coming weeks.”
Bell said that as of Tuesday, 58 cases had been reported in South Carolina, primarily in Spartanburg County in the northwest part of the state.
An outbreak along the Arizona and Utah border continues to grow. The Arizona Department of Health Services reported 153 cases this week, almost all in Mohave County.
Cases in Utah have reached 102, according to the state Department of Health and Human Services. While most of those cases are linked to the cluster on the Utah-Arizona border, the number of cases is also increasing near Salt Lake City. NBC affiliate KSL reported that eight students at a high school in Wasatch County had been diagnosed.
As of Wednesday, the CDC had reported 1,798 confirmed cases of measles in 42 states in 2025. Three people, an adult in New Mexico and two girls in Texas, have died.
