Comparison of RSV, influenza and COVID-19 clinical characteristics in hospitalized infants in Valladolid–Spain, 2010–2022

<bold>Introduction:</bold> We aimed to compare the clinical characteristics of all laboratory-confirmed Respiratory Syncytial Virus (RSV), influenza and COVID-19 hospitalized cases among infants aged ≤2 years in Valladolid during Jan2010–Aug2022 <bold>Methods:</bold> Retrospective cohort. Among RSV cases, we identified risk factors for hospitalization and for severity (length of hospital stay≥8 days, intensive care unit [UCI] admission, hospital readmission≤30 days and death). Using a multivariate logistic regression model, we compared severity between RSV and influenza and COVID-19 cases <bold>Results:</bold> We analyzed 1507 RSV (1274 hospitalized), 32 influenza and 52 COVID-19 cases. Hospitalized RSV (mean age 5.3 [SD 5.9], median age 3.0 months) and COVID-19 (4 [5.7], 1) were younger than influenza (9.1 [7.5], 8) cases. Risk factors for RSV hospitalization were prematurity (OR 2.55 [95%CI 1.43, 4.57]) and coinfection (2.00 [1.46,2.74]). Risk factors for RSV severity were prematurity (2.28 [1.64,3.17]), low birth weight (1.84 [1.15,2.95]), low weight at diagnosis (2.27 [1.40,3.67]), chronic lung (2.92 [1.54,5.52]), cardiovascular (6.89 [1.48,32.02]) or neurologic (3.89 [2.02,7.49]) disease and coinfection (2.62 [2.08,3.31]). RSV had higher severity vs influenza (adjusted OR 2.45 [1.03,5.96]) but did not show statistically significant differences vs COVID-19 <bold>Conclusions:</bold> Among infants, RSV hospitalization outcomes are more severe than influenza and generally comparable to those from COVID-19. Currently both influenza and COVID-19 vaccines are part of the maternal Spanish immunization program, RSV maternal vaccination could have a high clinical impact on protecting their children <6 months of age