Mesa latest hub of growing East Valley measles outbreak

Editor’s note: This story was published on Wednesday and updated on Friday after the Maricopa County Department of Public Health identified another positive measles case.

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Maricopa County announced three new measles cases on Wednesday and another on Friday connected to an East Valley outbreak, bringing the county’s total to 14 for the year so far.

On Wednesday, the county health department said 96% of cases are in unvaccinated individuals, but has not shared how many positive cases are children and whether any have suffered serious health effects. Measles is an incredibly contagious disease that can be especially dangerous to unvaccinated individuals, particularly very young children. Two doses of the measles-mumps-rubella vaccine is 97% effective at preventing the disease.

Fourteen positive measles cases are the most the county has had since at least 2006, according to data from the Arizona Department of Health Services. Maricopa County had no cases last year and two in 2024. Before this year, the most the county has seen over the last 20 years was five cases in 2022.

In total, the state has seen 311 positive measles cases since the start of 2025, most of them concentrated in the Northern Arizona community of Colorado City, a former Fundamentalist Mormon stronghold where vaccination rates are very low. Ninety-seven percent of cases have been in unvaccinated individuals, and two-thirds of positive cases have been minors. Twenty-four people have required hospitalization, but no one has died in the state due to measles.

The East Valley isn’t known for being a bastion of high vaccination rates, though far more of its population is vaccinated than in Colorado City. The outbreak there has grown slowly since January, when the county’s first measles case was announced. The county identified one positive case on Jan. 15 and two more on Jan. 23. By mid-April, the case count had grown to six. Now in early May, that figure has more than doubled.

The first exposure sites identified by county health officials were primarily in Gilbert and Queen Creek. Exposure sites for the more recent cases are all in Mesa. They include many highly trafficked locations, including a church, grocery store, a Target location and several fast food restaurants.

Here is the full list, courtesy of the county health department. Health officials say to watch for symptoms — such as a high fever, runny nose and red and splotchy rash — for up to 21 days. If you experience symptoms, stay home and call a medical provider.