At least 63 children are sick with measles in Ohio

An ongoing measles outbreak in central Ohio has ballooned to 63 cases as of Thursday. Twenty-five children have been hospitalized.

The state's health system is also fighting the surge in respiratory illness — flu, RSV and COVID-19. The high rates of those illnesses are making it harder for doctors to flag measles cases, Mysheika Roberts, the health commissioner in Columbus, Ohio, told ABC News.

"Measles can present an issue like a cold, like a mild RSV, or mild flu. And it’s not until that rash appears that most providers and parents say, oh, this is different," she said. "By that point, the case has already exposed other individuals, whether it’s at day care, at home, at church."

Three of the 63 children have received one dose of the measles, mumps and rubella (MMR) vaccine, a highly effective vaccine that protects against the three diseases. The remaining 60 children are unvaccinated. The majority of the children are under 5 years old.

The Centers for Disease Control and Prevention recommends that all children get two doses of the MMR vaccine — the first when they’re 12 to 15 months old and the second when they’re 4 to 6 years old. One dose is 93% effective against measles and two doses are 97% effective.

The vaccine’s effectiveness helped the United States officially eliminate measles in 2020, a designation that means the virus is no longer continuously circulating in the country. But there can still be periodic outbreaks if the virus is brought into a community where many people are unvaccinated. Rises in vaccine hesitancy over the past decade eroded MMR vaccination rates in some areas, which creates pockets in the U.S. particularly susceptible to measles spread.

For example, research showed that low vaccination rates were responsible for the 2015 Disneyland outbreak, which spread to over 125 people.

Roberts said that the children affected by the Ohio outbreak appear to be unvaccinated because their families rejected the vaccine, not because they had delays in their vaccinations as a result of the COVID-19 pandemic. The Columbus health department offers the vaccine at its clinic but the department hasn’t seen any uptick in the number of people seeking out the MMR vaccine in response to the outbreak, officials said.

It’s still not clear how large this outbreak could become. The health department doesn’t have good visibility into the percentage of people who are vaccinated against measles in the state of Ohio, Roberts said. Her team is working with the CDC, insurance providers and medical providers to get a better estimate of that number.

"Once we get that information about the population here in central Ohio, the CDC is optimistic they’ll be able to get us an estimate of how large this outbreak could get," she noted. "But at this point, just looking at past outbreaks in other communities, we’re just hoping that we don’t get as large as some of those."