New RSV prevention strategy for infants under study in bogotá

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * 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. * Exposure Eligibility Window: Infant born ≥5 weeks after the start of the RSVpreF maternal vaccination campaign in Bogotá, ensuring opportunity for maternal immunization. Exclusion Criteria: * 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. * Duplicate episodes: Readmission for the same respiratory episode ≤14 days after discharge (only the first episode will be included). * Delayed sampling: First respiratory sample obtained \>48-72 hours after initial admission to the health system. * Lethal congenital conditions: Congenital or genetic disorders incompatible with life or that substantially alter the expected clinical course. * Concurrent interventional study participation: Enrollment in another clinical trial that may affect respiratory outcomes. * Inability to establish mother-infant linkage due to adoption, loss of parental custody, or absence of biological maternal records.