Surging measles cases are ‘fire alarm’ warning that other diseases could be next

The rise in measles cases worldwide is a clear warning sign that other vaccine-preventable diseases could arise in the future, 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 vaccination coverage can trigger outbreaks, like a fire alarm going off when smoke is first detected. »

In other words, measles is often the first disease to appear when vaccination rates decline overall.

“When we see cases of measles, it indicates that gaps are almost certainly likely for other vaccine-preventable diseases like diphtheria, whooping cough or polio, even though they may not yet set off the fire alarm,” O’Brien said at a press briefing Monday, ahead of the release of the WHO report on progress toward measles elimination, published Friday in its Weekly Epidemiological Review.

Indeed, cases of whooping cough are also increasing in the United States and are on track to reach their highest level in a decade. More than 20,000 cases of whooping cough have been reported so far in 2025, according to the Centers for Disease Control and Prevention.

In 2024, there were an estimated 11 million measles infections worldwide, according to the report, almost 800,000 more than in 2019.

Last year, 59 countries reported large measles outbreaks. In 2025, the United States joined the list of countries.

Threatened elimination status

Ongoing outbreaks threaten the measles elimination status of some countries.

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.)

A total of 81 countries had reached elimination status by 2024, according to the WHO. Canada eliminated measles in 1998. Two years later, the United States did the same.

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 the outbreak.

But U.S. vaccination rates 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 vaccines like those for measles, mumps and rubella.

The main determining factor for a country losing its measles elimination status is the continued spread of the same strain of the virus for a full year.

Canada reached that threshold this month. The United States could be next to follow if scientists can trace current cases back to an outbreak that began in Texas in January.

Nearly all samples analyzed from these early cases were identified as a measles genotype called D8, according to a CDC report released in April.

The D8 genotype was recently detected during an outbreak in South Carolina.

Preliminary results from samples sent from South Carolina to CDC labs “are of the same type, D8, as 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 definitively link the Texas outbreak to 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 these results in the coming weeks.”

Bell said that as of Tuesday, 58 cases had been reported in South Carolina, mostly in Spartanburg County in the northwest part of the state.

An outbreak along the Arizona-Utah border continues to grow. The Arizona Department of Health Services reported 153 cases this week, almost all of them in Mohave County.

Cases in Utah have reached 102, according to the state Department of Health and Human Services. While the bulk of these 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 Wasatch County high school 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 little girls in Texas, have died.