Measles Outbreak in Chicago Migrant Shelter Reveals at Least 28 Percent Were Vaccinated

Following identification of 15 cases of measles in a Chicago shelter that houses migrants from Venezuela, city public health officials announced on Mar. 20, 2024 that “measles is circulating in our city. And it’s why we are putting a call out for everyone who is at risk to protect themselves now” by getting a measles-mumps-rubella (MMR) shot.¹ On Apr. 23, the Commissioner of the Chicago Department of Public Health told doctors to consider giving children living in the city a second dose of MMR vaccine “earlier than usual,” warning that “too many Chicagoans are still not vaccinated against this highly contagious virus and other vaccine preventable diseases.”²

On May 16, officials at the U.S. Centers for Disease Control and Prevention (CDC) published a report that a total of 57 confirmed measles cases had been confirmed in residents of the city migrant shelter or close contacts, and that 16 of the cases (28 percent) had received one or two doses of measles vaccine “more than 21 days before first known exposure,” while 41 cases (72 percent) “did not have documentation of measles vaccination and were considered unvaccinated.”³

CDC officials admitted that during the spring 2024 measles outbreak among mostly Venezuelan migrants at the Chicago shelter, “the percentage of measles cases among persons with a history of previous vaccination was higher than that reported through recent national surveillance in the United States.”⁴ They blamed the nearly 30 percent measles vaccine failure rate on “prolonged or close exposure to measles virus” among residents of the crowded shelter and said that Venezuela had seen a drop in first-dose measles vaccination coverage for children twelve months and older from 95 percent to 68 percent between 2017 and 2021 because of worldwide “disruption of routine immunization services during the COVID-19 pandemic.” They also defended the effectiveness of the MMR vaccine by repeating the often-quoted mantra that “primary vaccine failure occurs in approximately 4% of recipients of 1 MMR dose and is rare among recipients of 2 MMR doses.”⁵

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