The World Health Organization warned on Friday that rising measles cases around the world are a stark warning sign that outbreaks of other vaccine-preventable diseases could be next.
“It is important to understand why measles is so important,” said Dr Kate O'Brien, director of the WHO Department of Immunization, Vaccines and Biologicals. “Its high transmissibility means that even a small drop in vaccination coverage can trigger outbreaks, like when smoke is first detected and the fire alarm goes off.”
That is, measles is often the first disease to arise when there is a general drop in vaccination levels.
“When we see cases of measles, it signals that there are almost certainly gaps in other vaccine-preventable diseases such as diphtheria, whooping cough or polio, even though they may not yet set off fire alarms,” O'Brien said at a media briefing on Monday ahead of the release of a WHO report on progress in eliminating measles published Friday in his journal. Weekly Epidemiological Report.
Indeed, the United States is also on the rise in whooping cough cases and is on track to become most in a decade. More than 20,000 cases of whooping cough were reported in 2025, according to the Centers for Disease Control and Prevention.
There were nearly 11 million measles cases reported worldwide in 2024, nearly 800,000 more than were reported in 2019, according to the report.
Last year, 59 countries reported major measles outbreaks. In 2025, the United States joined the list of countries.
Exclusion status in jeopardy
Ongoing outbreaks threaten the so-called measles elimination status of some countries.
Elimination means that the virus has stopped spreading in a particular country or region. (Only one virus, smallpox, has been eradicated or destroyed forever worldwide.)
A total of 81 countries have reached elimination status in 2024, according to WHO. Canada eliminated measles in 1998. Two years later, the United States did the same.
Elimination status means the country has the ability to stop an outbreak when measles cases arrive from overseas, O'Brien said. If vaccination rates are high enough, the virus will not be able to infect enough unvaccinated people to stop the outbreak.
But vaccination rates in the US are falling: An. NBC News Investigation found that since 2019, 77% of counties and jurisdictions reported a decline in the number of children receiving routine childhood immunizations, such as measles, mumps, and rubella.
A key factor in determining whether a country loses measles elimination status is the continued spread of the same strain of the virus throughout the year.
Canada has reached this 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 samples analyzed from these early cases were identified as having a measles genotype called D8, according to the study. CDC report published in April.
Genotype D8 was recently discovered in an outbreak in South Carolina.
Preliminary results from samples sent from South Carolina to CDC laboratories “are of the same type, D8, seen elsewhere in the United States,” Dr. Linda Bell, state epidemiologist for the South Carolina Department of Public Health, said at a briefing Tuesday.
Additional genetic sequencing is needed to establish a definitive link between the outbreak in Texas and South Carolina and the outbreaks in Utah and Arizona. A South Carolina Department of Public Health spokesperson said the agency “expects these results in the next few weeks.”
Bell said there were 58 cases reported in South Carolina as of Tuesday, mostly in Spartanburg County in the northwestern part of the state.
An outbreak on the Arizona-Utah border continues to grow. Arizona Department of Health Services there have been 153 cases reported this week, almost all in Mohave County.
The number of cases in Utah has reached 102, the department said. State Department of Health and Human Services. While the bulk of those cases are linked to a cluster on the Utah-Arizona border, cases are also rising near Salt Lake City. NBC affiliate KSL reported that eight high school students in Wasatch County had been diagnosed.
As of Wednesday, the CDC reported 1,798 confirmed cases of measles in 42 states in 2025. Three people, an adult in New Mexico and two little girls in Texas, died.
