Key Points, updated: 4/4/2025

•  Overall acute respiratory illness activity level in Chicago remains Low. Flu, COVID-19 and RSV activity remain Low.  
• ED visits, hospitalizations, and ICU admissions for flu, RSV, and COVID-19 continue to decrease across nearly all age groups. 
• The percentage of specimens that tested positive for flu continues to decrease from a peak of 23% in January. Detections of flu B represent 77.8% of all reported flu detections last week. Among flu A specimens that were subtyped for the week 71% were H1N1. Test positivity for RSV has been decreasing since mid-December and continues to decrease. Test positivity for COVID-19 decreased from the previous week.
• Compared to baseline concentrations, the overall wastewater concentrations for flu A, flu B, and RSV remain moderate; COVID-19 wastewater concentration decreased from low tois minimal. It is possible that even as clinical surveillance indicators (e.g., ED visits and hospitalizations) decrease, wastewater data may fluctuate for longer and decrease over an extended period of time because of the persistence of viral shedding from infected persons and/or in wastewater systems.  
• In the continental US, the RSV season ended March 31, 2025. Infants and children should no longer receive nirsevimab this respiratory season. See the CDPH HAN for more details.
• The CDC has issued interim estimates of 2024-25 Seasonal Influenza Vaccine Effectiveness (VE) and 2024-25 COVID-19 VE, which suggest that this season’s influenza and COVID-19 vaccines were effective in preventing medically-attended illness, including hospitalization, in the US. 
• Flu and COVID-19 vaccine coverage across the city remain low. See CDPH’s Mid-Season Seasonal Respiratory Vaccine Coverage Report for more details.
• For information on the national bird flu outbreak, see the CDPH H5N1 Bird Flu webpage and the CDPH HAN: Flu Page for clinicians.