Health officials are investigating a measles outbreak in several childcare facilities in the Columbus area of central Ohio. There are currently 18 cases under investigation, Kelli Newman, a spokesperson for Columbus Public Health, told CBS News Wednesday. 

All of the cases are in unvaccinated children, and 17 of the 18 infected children are under the age of five, an age group particularly susceptible to serious health complications from measles, according to the Centers for Disease Control and Prevention. Seven of the children have been hospitalized, Newman said. 

The outbreak is affecting seven day cares and one school, Newman said. When the investigation first began on Nov. 9, in conjunction with Franklin County Public Health, just one child care facility was affected, and only four cases were confirmed at the time, according to a press release from the CPD. 

“All the facilities are cooperating with public health, and they have notified all parents and removed all unvaccinated students out of the facility for 21 days after the last case onset,” Newman said in a statement. “We continue to work on contact tracing with Nationwide Children’s Hospital and with affected families. Our investigation and contact tracing is ongoing and we don’t know yet where the outbreak started.” 

Franklin County, where Columbus is located, also confirmed four other measles cases in the summer of 2022, according to the CPD press release. The press release did not mention any possible link between the cases. 

Measles spreads easily by coughing, talking or being in the same room with an infected person, according to the CDC. The virus is highly contagious and symptoms begin around eight to 12 days from the date of first exposure. Symptoms to watch out for include fever, a cough, runny nose, watery eyes and a rash that begins two or three days after the fever begins and spreads from the head to the rest of the body. 

About one in five people who contract the measles will be hospitalized, the CDC says. In young children, serious complications can include pneumonia — affecting about one in 20 — and encephalitis, a form of brain swelling that affects as many as one in 1,000 children, and can lead to convulsions and lifelong complications. 

Measles is preventable and has previously been declared eliminated in the United States, thanks to a “highly effective vaccine program,” the CDC said. 

Newman and other public health officials have encouraged parents to make sure their children are up to date on childhood vaccinations, especially the two-dose MMR vaccine, which can prevent mumps, measles and rubella. According to the CDC, children typically receive their first shot between 12 and 15 months, and the second shot between four and six years old. 

“One dose of MMR provides 90% protection and two doses provide 97% protection against measles,” Newman told CBS News. 

Adults can also be vaccinated for the measles if they were not vaccinated as children. 

“Measles is both highly contagious and preventable,” said Joe Mazzola, Franklin County Health Commissioner, in a press release. “It can be a severe illness, so we strongly encourage anyone who has not been vaccinated to get vaccinated to prevent further spread.”