• An unvaccinated person exposed numerous individuals to measles at the St. Louis Aquarium on April 30, prompting a public health response.
• St. Louis exhibits low MMR vaccination rates, particularly among kindergarteners, falling significantly below state and national averages and herd immunity thresholds.
• Health officials emphasize the importance of vaccination, address access barriers, and combat misinformation to prevent measles outbreaks, with the St. Louis Metropolitan Pandemic Task Force reactivated to prepare for potential spread.

On April 30, 2025, an unvaccinated individual from Illinois visited the St. Louis Aquarium at Union Station, potentially exposing numerous people to measles. This incident has heightened concerns among health officials due to already low MMR vaccination rates in the St. Louis area, especially among kindergarteners. The situation is further complicated by a rise in measles cases nationally, making the region particularly vulnerable. Health departments are working to contact potentially exposed individuals and urge vaccination to prevent further spread.

• What: Potential measles exposure at St. Louis Aquarium due to an unvaccinated individual and a rise in measles cases nationally coupled with low local vaccination rates.
• Who: The key individuals/entities include: Unvaccinated Illinois resident, Visitors to St. Louis Aquarium, St. Louis Department of Health, Missouri Department of Health and Senior Services, Dr. Mati Hlatshwayo Davis, and local kindergarteners.
• When: The exposure occurred on April 30, 2025, between 1-6 p.m. Symptoms develop 11-14 days post-exposure.
• Where: The primary location is the St. Louis Aquarium at Union Station. Other locations mentioned include Taney County and New Madrid County, MO, Southern Illinois, and various Missouri counties with low vaccination rates.

The measles exposure at the St. Louis Aquarium underscores the vulnerability of the region due to low vaccination rates. The decline in MMR vaccination rates since the COVID-19 pandemic has created an environment ripe for outbreaks. The situation is further complicated by misinformation surrounding vaccines and barriers to healthcare access, especially in urban areas like St. Louis. The re-establishment of the St. Louis Metropolitan Pandemic Task Force indicates the seriousness with which health officials are treating the potential for a measles outbreak. Addressing vaccine hesitancy, improving access to healthcare, and promoting accurate information are crucial steps in mitigating the risk.

"When discussing St. Louis’ low rates, the city’s different socio-demographic composition plays a factor, since some City residents face barriers to care, including being under/uninsured, lacking transportation, or difficulties affording a visit to the clinic."

"We are, epidemiologically, absolutely at risk for measles. We know when the measles immunization rates dip below 95%, we are absolutely at increased risk. Currently, those numbers are at least 5 points too low. That can make a huge difference."

"Please note that a rash may not develop for several days. So please, do not wait for one to appear if you are experiencing any of the other listed symptoms."

The measles exposure at the St. Louis Aquarium serves as a stark reminder of the importance of vaccination and public health preparedness. With measles cases rising nationally and vaccination rates lagging in certain areas of Missouri, proactive measures are essential. Ongoing efforts to educate the public, combat misinformation, and improve access to vaccination services will be critical in preventing a potential outbreak and protecting vulnerable populations. The situation remains fluid, and continued monitoring and communication from health officials are necessary.