Nine of those infected were hospitalized and more cases are likely, health authorities said. U.S. vaccination rates for measles are falling, according to the CDC.

As of Tuesday, 22 children and two adults had been infected, all of whom were unvaccinated, local officials said.

Measles is marked by high fevers and a telltale rash. People can spread the infection from four days before the rash develops to four days afterward. In addition to the miserable illness, measles can cause complications, particularly in children younger than 5, pregnant people, adults over the age of 20, and people with compromised immune systems.