Key Points, updated: 4/18/2025

• Overall acute respiratory illness activity level in Chicago remains Low.Flu and RSV activity remain Low and COVID-19 activity remains minimal.
• ED visits, hospitalizations, and ICU admissions for flu, RSV, and COVID-19 remain low across most age groups.
• The percentage of specimens that tested positive for flu continues to decline from a peak of 23% in late January. Of all influenza positive specimens last week, the vast majority (89%) were associated with flu B. Test positivity has been decreasing since mid-December for RSV and decreasing since late February for COVID-19. 
• Compared to baseline levels, overall wastewater concentrations for flu A increased from moderate to high, flu B declined to minimal, RSV and COVID-19 remain minimal. 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.