Hamilton County Public Health is asking residents to verify their measles vaccination status as the U.S. records its highest case count since 1991.

The county health department published the advisory on Sept. 8, warning that outbreaks are growing more frequent in Ohio and neighboring states. No confirmed measles cases in Hamilton County were cited in the announcement, but the department said it is monitoring for local spread. The advisory applies to all county residents, including families in the Sharonville, Springdale, Evendale and Woodlawn communities.

Nationally, the outbreak has reached 2,777 confirmed cases, according to the Center for Infectious Disease Research and Policy (CIDRAP) at the University of Minnesota. That figure already exceeds the 2,289 cases recorded in all of 2025. Among this year's patients, 94% are unvaccinated or have unknown vaccine status, and two-thirds are children and teenagers, according to CIDRAP citing CDC data.

Ohio alone has confirmed 142 cases across 15 counties, an increase of 73 in a single week. The state recorded 45 cases in all of 2025 and just seven in 2024, according to the Akron Beacon Journal citing Ohio Department of Health data.

Declining vaccination rates are fueling the surge. Ohio Department of Health Director Dr. Bruce Vanderhoff said on Aug. 4 that the rate of kindergartners in the state who met all vaccine requirements dropped from 89.9% to 85.4%, as reported by Fox 8 Cleveland. Nationally, kindergarten vaccination coverage fell from 95.2% in the 2019–20 school year to 92.5% in 2024–25, below the 95% threshold needed for herd immunity, according to the Beacon Journal citing CDC figures.

In a July 30 statement, Vanderhoff urged vaccination. "It's unfortunate that these outbreaks have become more common in Ohio over the past few years, because this disease is preventable," he said. "… I strongly encourage you to protect yourselves and your children by getting vaccinated."

The two-dose MMR (measles, mumps and rubella) vaccine series is 97% effective at preventing measles. One dose is 93% effective. Most vaccinated people are protected for life, and those who do contract the virus after vaccination tend to experience milder illness, according to the health department. Measles vaccinations are covered by most health insurance plans, including Affordable Care Act (ACA) marketplace plans.

Measles spreads through coughing, sneezing and talking. The virus can linger in the air for up to two hours after an infected person leaves a room. A single infected person can spread the disease to up to 90% of unvaccinated people they encounter, according to the health department.

Residents unsure of their vaccination history can contact Hamilton County Public Health's customer service team at (513) 946-7800 or submit an online immunization records request at hamiltoncountyhealth.org.