Respiratory Syncytial Virus Risk Profile in Hospitalized Infants and Comparison with Influenza and COVID-19 Controls in Valladolid, Spain, 2010-2022

Introduction: We aimed to describe the risk profile of RSV infections among children aged ≤ 24 months in Valladolid from January 2010 to August 2022 and to compare them with influenza and COVID-19 controls.

Methods: We conducted a retrospective cohort study of all laboratory-confirmed RSV, influenza, and COVID-19 infections. We analyzed risk factors for RSV hospitalization and severity (length-of-stay ≥ 8 days, intensive-care-unit admission, in-hospital death or readmission < 30 days) and compared severity between hospitalized RSV patients vs. influenza and COVID-19 controls using multivariable logistic regression models.

Results: We included 1507 patients with RSV (1274 inpatient), 32 with influenza, and 52 COVID-19 controls. Hospitalized RSV (mean age 5.3 months) and COVID-19 (4 months) were younger than influenza (9.1 months) patients. Sixteen percent of patients had RSV within the first month of life. Most infants did not have comorbidities (74% RSV, 56% influenza, and 69% COVID-19). Forty-one percent of patients with RSV and influenza were coinfected vs. 27% COVID-19 (p = 0.04). Among RSV, hospitalization risk factors were prematurity (adjusted OR 3.11 [95% CI 1.66, 4.44]) and coinfection (2.03 [1.45, 2.85]). Risks for higher severity were maternal smoking (1.89 [1.07, 3.33]), prematurity (2.31 [1.59, 3.34]), chronic lung disease (2.20 [1.06, 4.58]), neurodevelopmental condition (4.28 [2.10, 8.73]), and coinfection (2.67 [2.09, 3.40]). Breastfeeding was protective against hospitalization (0.87 [0.80, 0.95]) and severity (0.81 [0.74, 0.88]), while complete vaccination schedule was protective against severity (0.51 [0.27, 0.97]). RSV had 2.47 (1.03, 5.96) higher risk of experiencing any severe outcome compared to influenza and did not show significant differences vs. COVID-19.

Conclusions: RSV hospitalizations were more frequent and severe than influenza, while severity was comparable to the early pandemic COVID-19. Currently, both influenza and COVID-19 vaccines are included in the maternal and childhood Spanish immunization schedule between the ages of 6 and 59 months. RSV monoclonal antibody is recommended for ≤ 6 months but a third of patients were aged 6-24 months. Maternal RSV vaccination can protect their children directly from birth and indirectly through breastfeeding.