MESA, AZ — Public health officials in Maricopa County say they are confronting the most significant measles outbreak the region has seen in 30 years, with 15 confirmed cases so far in 2026. This includes eleven potential exposures tied to a recent outbreak traced back to exposures beginning April 23.

Two key exposure events took place at the Arizona Athletic Grounds in southeast Mesa, one on April 23 and another spanning May 5-7, according to the county health department. Officials have posted a complete list of exposure locations on their website for residents to review.

Measles is considered highly contagious, often beginning with symptoms such as high fever, cough, runny nose, and watery eyes before progressing to its distinctive rash.

“We’re obviously alarmed that we’re seeing transmission of the measles virus within the community,” said Dr. Wassim Ballam, chief of infectious diseases at Phoenix Children’s Hospital. He expressed concern that vaccination rates have fallen below 90 percent in the Phoenix metro area, noting the Centers for Disease Control and Prevention once considered measles virtually eradicated in the U.S.

“[The] major tool is the vaccine. We have a highly effective vaccine — we’re talking more than 95 percent efficacy with the two doses,” Ballam said, urging parents and other residents to ensure they are up to date.

While measles primarily affects children ages five and younger, unvaccinated adults are also at risk. Dr. Nick Staab, Maricopa County’s chief medical officer, warned that the current low immunization rates could lead to sustained transmission.

“That low immunization rate means the potential for ongoing transmission in the community is there,” Staab said. “This is a large outbreak for us here in Maricopa County. It’s certainly something we’ve not dealt with in a long period of time.”

For those choosing not to vaccinate, Staab advised closely monitoring for symptoms and isolating for 14 days if they appear, to prevent further spread.