This study aims to evaluate the real-world effectiveness of two preventive immunization strategies against Respiratory Syncytial Virus (RSV)-associated severe acute respiratory infection in infants less than six months of age in Bogotá, Colombia. The strategies include maternal vaccination with RSVpreF administered between 28 and 36 weeks of gestation and neonatal immunization with nirsevimab for infants born to mothers who did not receive RSVpreF during pregnancy. Using a test-negative case-control design embedded in the city's sentinel surveillance system, infants hospitalized for severe respiratory infection will be systematically tested for RSV. Comparative vaccine effectiveness will be estimated to determine the impact of maternal RSV vaccination and neonatal monoclonal antibody immunization on RSV-associated hospitalizations, intensive care admissions, and mortality. The study will generate real-world evidence to inform local and regional public health decisions and guide the implementation of cost-effective hybrid immunization strategies against RSV in middle-income settings.
Age: Infants younger than 6 months at the time of hospital admission.
Residence: Maternal residence in Bogotá, Colombia, verified through clinical record, identification document, or health system registry.
Clinical Condition: Hospitalization due to severe acute respiratory infection (SARI) meeting the district operational definition (presence of fever, cough, and/or signs of respiratory distress, requiring inpatient management).
Laboratory Testing: Respiratory specimen collected and tested for RSV by RT-PCR or validated antigen test within ≤48 hours of hospital admission, or repeated within 24-48 hours if initial test is negative.
Prematurity: Infants born at ≤32 weeks of gestation.
Healthcare-associated respiratory infection: Symptom onset >48 hours after hospital admission for another condition.
Non-respiratory hospital admission: Primary reason for hospitalization unrelated to respiratory disease (e.g., trauma, elective surgery).
Vaccination status unverifiable: Inability to confirm maternal RSVpreF vaccination status after reasonable attempts to verify through registry, vaccination card, or prenatal documentation.