New study finds a high number of measles cases are misdiagnosed

Nearly 7 percent of U.S. measles cases are misdiagnosed at least once in the two weeks before a doctor’s diagnosis, an alarming new study has found.

Of 4,651 cases reported between 2001 and 2023, 381 were misdiagnosed, the University of Iowa assessment of private and federal insurance databases revealed.

The findings suggest the “not uncommon” delays could be helping to facilitate transmission of the world’s most contagious virus amid a historic national resurgence – especially in outpatient clinics and hospital waiting rooms.

“Delays occurred most frequently in outpatient settings” at 81 percent, the researchers wrote, noting that the virus can remain airborne for hours.

Some groups are more affected than others, too, including patients who received respiratory antibiotic prescriptions and those who were under 2 years old who may not be able to discuss their symptoms with doctors.

Doctors who have never seen a case of the measles – previously eliminated in the U.S. in 2000 – may not initially incorporate measles in diagnoses they consider, the researchers also noted.

A growing problem

Measles is continuing to spread in Pennsylvania, Wisconsin and Florida.

There have been 4,852 confirmed cases nationally this year, according to federal data, though Pennsylvania updated its own case tally to a total of 1,433 on Monday. That’s more than double the 2,289 cases recorded in 2025.

The spread has been tied to outbreaks in under-vaccinated communities, and all of the year’s deaths have been reported in the state of Pennsylvania – and in people who were unvaccinated.

Two doses of the vaccine against measles, which also targets the mumps and rubella viruses, are 97 percent effective against infection, offering lifelong protection.

Without the shots, infections – which are also transmitted from person to person – can lead to life-threatening brain swelling, pneumonia and fever, as well as ear infections and a rash.

Unfortunately, MMR vaccinations have fallen, according to both state and federal data.

Vaccine coverage among kindergarten-aged children decreased in more than half of states between the 2024-2025 and 2025-2026 school years, according to the Johns Hopkins Bloomberg School of Public Health.

“Idaho – where one-quarter of all children are unprotected against measles, mumps and rubella – reported the largest drop: more than 3 percentage points (from 78.5 percent to 75.2 percent). Louisiana and Virginia each saw decreases of about 2 percentage points,” the school said.