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A measles vaccine is given to a person.

Chicago Department of Public Health officials declared the recent measles outbreak as over.

AP file

Chicago measles outbreak, worst in the U.S., is over

Since the first reported case on March 7, over 30,000 vaccines have been administered, primarily to migrants in shelters.

City public health officials say the measles outbreak, the largest in the U.S., is officially over nearly three months after cases were detected at migrant shelters.

Chicago and the surrounding area accounted for the majority of the country’s measles cases this year after cases were discovered at a migrant shelter in Pilsen in March.

Over the next several months, a total of 64 cases were detected throughout the city. Illinois had just five cases in 2023, which were the first in the state since 2019.

As of last week, there were a total of 142 measles cases across the U.S. Nineteen other states reported cases, though there were only nine other areas of the country reporting outbreaks of three or more infections.

The city’s top health official encouraged Chicagoans to get vaccinated.

“Our goal is the elimination of measles in Chicago and everywhere,” said Public Health Commissioner Olusimbo Ige. “With proper vaccination coverage, we know that zero is possible.”

Since the first reported Chicago case on March 7, more than 30,000 vaccines have been administered, primarily to migrants in shelters.

The most recent case was recorded on April 20.

Most cases appear in unvaccinated individuals, particularly young children. More than half the recorded cases in Chicago were in children younger than 5.

Despite a high vaccination rate, Chicago became a susceptible area to the extremely contagious disease.

A crowded migrant population in shelters combined with a tendency for low vaccination rates in their home countries became a breeding ground for measles, said Dr. Allison Bartlett, a University of Chicago professor and infectious disease specialist.

“The shelter-associated outbreak was a combination of both an initial case in an unvaccinated individual, combined with a congregate living situation that made it incredibly easy to spread among a population of incompletely vaccinated individuals,” she said.

After the outbreak began, the city health department began vaccinating migrants before they were placed in shelters.

According to public health officials, the “vast majority” of new arrivals are already vaccinated or accept a vaccine.

Measles symptoms generally appear 10 to 14 days after exposure. Common symptoms include fever, cough, runny nose, and red or watery eyes, according to the U.S. Centers for Disease Control and Prevention.

A rash can appear three to five days after initial symptoms begin.

“This really was a public health success in terms of ending the outbreak, but we remain at risk at all times for additional measles cases,” Bartlett said.

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