A measles outbreak continues to hit Chicago, while surveillance nationally found 113 cases in 18 states as of April 4, 2024. With cases both in the community and in migrant shelters, the Chicago Health Department reported 61 measles infections as of April 11, 2024.
According to the Centers for Disease Control and Prevention (CDC), 83% of the cases nationally were either unvaccinated or had unknown vaccination status. There have been seven outbreaks (defined as three or more related cases) reported in 2024, and 73% of cases (83 of 113) are outbreak-associated.1
No vaccine is perfect, and 12% of the cases with a history of one dose of measles-mumps-rubella (MMR) vaccine acquired measles. Moreover — since high levels of immunity in the general public have been used to rationalize letting unvaccinated children still come to school — it should be underscored that 5% of the 2024 cases had a history of two doses of MMR vaccine.
Also busted was the myth that seems to be driving some of this: that measles is such an inconsequential infection that parents in the pre-vaccine days used to have exposure parties for their children. Consider these CDC data, which include all but a few of the Chicago cases because of differences in the surveillance timeline: 58% (65 of 113 cases) were hospitalized for isolation or for management of measles complications. Of those 65 hospitalized cases, 37 were under the age of 5 years, nine were ages 5 to 9 years, and 19 patients were aged 20 years and older. No deaths have been reported.
Chicago health officials have administered 13,622 doses of vaccine since March 7, 2024, including 494 shots on April 8, 2024.2 The average is running at more than 300 immunizations per day. The city has opened walk-in immunization clinics where the MMR vaccine is provided for no out-of-pocket cost to any child 0 to 18 years of age and uninsured adults 19 years of age and older.
The vaccine is effective up to 72 hours after exposure to measles as a post-exposure prophylaxis. The health department is alerting people that if they were at a given location on a certain date, they may been exposed to measles. These locations include schools, city buses, shopping centers, and pharmacies.
“For healthcare facilities, now is the time to be refreshing awareness,” said Michael Bell, MD, acting director of CDC’s division of healthcare quality promotion, at a briefing. “I think this needs to include not just clinical staff, but whoever is manning the reception intake areas, your front desk, and also patient evaluation staff who need to know what to do. Just like with COVID, we [need to] alert people to notify the clinical staff before they arrive.”
Review procedures for follow-up after suspected exposures, staff immunity status, and policies for family members and visitors of measles patients, he recommended.
“My standard admonition is if you’ve got someone with a fever and a rash sitting in your waiting room, that’s a mistake — right?” Bell said. “They shouldn’t be sitting there languishing and breathing around other people. You need to get a mask on them as soon as possible and get them into a separate room. If you do suspect measles in a hospital, isolate these patients in a negative pressure room.”
Healthcare workers should wear a respirator at least at the level of an N95 and patients should be masked for source control if they leave the room.
The CDC released a separate data set revealing that from Jan. 1, 2020, to March 28, 2024, a total of 338 U.S. measles cases were reported. Strikingly, 29% of those cases occurred during the first quarter of 2024, almost all in persons who were unvaccinated or whose vaccination status was unknown.
“Risk for widespread U.S. measles transmission remains low because of high population immunity,” the CDC concludes.3 “Enhanced efforts are needed to increase routine U.S. vaccination coverage, encourage vaccination before international travel, identify communities at risk for measles transmission, and rapidly investigate suspected measles cases to reduce cases and complications of measles.”
With routine childhood immunizations disrupted by the pandemic and the false attacks on vaccine safety, herd immunity has slipped slightly. For example, it was estimated at the CDC meeting that about 250,000 kindergarteners currently are susceptible to measles.
REFERENCES
- Centers for Disease Control and Prevention. Measles cases and outbreaks. Updated April 5, 2024. https://www.cdc.gov/measles/cases-outbreaks.html
- Chicago Department of Public Health. Measles update. Updated April 11, 2024. https://www.chicago.gov/city/en/depts/cdph/supp_info/infectious/get-the-facts--measles.html#dashboard
- Mathis AD, Raines K, Masters NB, et al. Measles — United States, January 1, 2020 –March 28, 2024. MMWR Morb Mortal Wkly Rep 2024;73:295-300.
A measles outbreak continues to hit Chicago, while surveillance nationally found 113 cases in 18 states as of April 4, 2024. With cases both in the community and in migrant shelters, the Chicago Health Department reported 61 measles infections as of April 11, 2024.
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