DETROIT — A Michigan baby who is now infected with measles had one dose of an MMR vaccine the day before she traveled through an airport where another person was contagious, health officials said.

The 12-month-old girl, who has the first documented measles case in Ingham County since 1994, traveled out of state with her family. Still, there wasn't enough time between her immunization and her exposure to the virus for the vaccine to fully trigger her immune system and protect her from getting sick, Dr. Nike Shoyinka, the county's medical health officer, said during a news conference on April 15.

"Usually, what we expect is that our body's immune system ... would have developed full immunity at about a two-week mark" after vaccination, Shoyinka said. "Even though this child was vaccinated, she was still relatively susceptible given the short period of time. However, I will say that this child's symptoms were very mild ... presumably because she had received at least one dose."

The MMR vaccine, a combination vaccine that protects against measles, mumps, and rubella, has been instrumental in curtailing the spread of measles. The Centers for Disease Control and Prevention recommends two doses of the MMR vaccine for children.

Shoyinka said health officials have communicated with the family and praised the information they provided "about potential exposures, about where they've been."

"I want to also emphasize that they did exactly what they were supposed to do in terms of making sure that their child was protected as they took her out of state," Shoyinka said. "This individual is doing well currently and is isolating at home with family."

The U.S. continues to battle the largest spike in measles cases since 2019, when more than 1,200 measles cases and 22 measles outbreaks were reported, according to the CDC. As of April 11, the CDC has confirmed over 700 measles cases in two dozen states in 2025.

The girl visited one of the two Michigan airports where a Kent County traveler exposed potentially hundreds of others to measles in late March — Detroit Metropolitan Airport in Romulus, Michigan, and the Gerald R. Ford International Airport in Grand Rapids, Michigan — Shoyinka said, though she did not specify which airport the child visited or exactly when.

"It's unclear at what point the exposure happened during that trip," she said, noting that health officials are still investigating whether the cases are epidemiologically linked.

"We are looking at specimen samples and we have sent them all the way to the CDC in order to identify matches to figure out where the exposure happened," Shoyinka added.

The Ingham County Health Department issued a news release April 10 detailing multiple exposure sites in Lansing, East Lansing, and Okemos from April 4 to April 8 where the girl went with loved ones while potentially infectious. But the health department did not disclose that the child also attended a Lansing day care/preschool over several days in early April, exposing about 50 other children, along with staff members and other visitors.

"We are matching records with every single child and every single family in there to make sure that we can communicate with them (about) what they need to do" to protect themselves and their children, Shoyinka said of the health department's contact tracing efforts. "If a child was unvaccinated, then we would monitor them for 21 days following the last date of exposure."

The school's name was not publicly disclosed but Shoyinka said health officials were working closely with the school. The school also provided a list of students, staff members, and other people who were at the site, according to Shoyinka.

The Ingham County child is the fifth person in Michigan to contract the measles this year, the state health department reported, and it comes amid an exploding number of cases in the U.S.

As of April 11, there were 712 confirmed measles cases in the U.S. this year in 24 states — more than double the number of cases nationally in all of 2024, when there were 285, according to the CDC. Of the cases this year, 32% were reported in patients under 5 while 38% were reported in those between 5 and 19, the CDC said.

The agency also reported 79 hospitalizations, including 45 patients who were under 5.  Most measles cases, 97%, occurred in unvaccinated patients or whose vaccination status is unknown, according to the CDC.

In an update on April 15, the Texas Department of State Health Services reported that more than 560 measles cases have been reported in the state since late January. Of those cases, 58 patients were hospitalized.

The CDC has confirmed two deaths from measles in the U.S. this year, which include two unvaccinated children with no known underlying health conditions in Texas. A third death remains under investigation.

Measles can cause serious illness, long-term disability, and death in people of all ages.

About 1 in 20 children with measles develops pneumonia. Roughly 1 out of every 1,000 children with measles infections will also have encephalitis. Brain swelling from encephalitis can lead to convulsions, permanent hearing loss, intellectual disability, and death, according to the CDC.

Anywhere from 1 to 3 of every 1,000 children with measles die from respiratory or neurologic complications from the virus.

People who contract measles during pregnancy are also more likely to develop pneumonia and require hospitalization. The virus can cause miscarriage and stillbirth as well as trigger preterm birth and lead to lower birth weights, according to the CDC.

"Our recommendation is for everyone to be vaccinated," Shoyinka said.

One dose of the MMR vaccine provides about 93% protection against the virus, and two doses offer about 97% coverage, according to the CDC.

"We're really encouraging everyone to contact their primary care provider if they're not sure about their vaccination status," Shoyinka said. "If they have received one dose in the past, then we're asking them to get another one. If they have not received any, then they need to start their vaccinations as soon as possible."

According to the CDC, measles symptoms typically start within seven to 14 days of exposure, but also have been known to appear as long as 21 days after initial exposure and can include:

Health officials urge anyone who may have been exposed to measles to monitor for symptoms for 21 days after the date of potential exposure. If symptoms develop, call ahead before visiting a doctor, urgent care center, or hospital emergency department to ensure precautions can be taken to avoid exposing others.