Study participants were characterized at Baseline by history of bronchopulmonary dysplasia, history of prematurity (less than or equal to 35 weeks gestational age), children with hemodynamically significant congenital heart disease (CHD), the presence of cohabitants less than 6 years old, possible exposure to indoor tobacco smoke, day care attendance, asthmatic or atopic mother, smoking during pregnancy, breastfeeding, prenatal assistance (4 or more visits during pregnancy), neonatal hospitalization care, history of neonatal assisted ventilation, and mother education level (completed primary school).

The number of participants with hospitalizations due to lower respiratory tract infection (LRTI) and hospitalizations due to lower respiratory tract infection caused by RSV.

Participants with hospitalization due to LTRI and hospitalization due to LTRI and RSV.

Variables that could act as risk factors for hospitalization for lower respiratory tract infection were tested in univariate and multivariate Poisson regression models. Baseline characteristics, such as age, gender, birth weight and comorbidities were included as covariates in the Poisson regression model. Variables for multivariate analysis were added applying forward selection. Gestational age and birth weight were included as continuous variables, considering that the higher they were the better they could act as a protection factor for hospitalization due to respiratory infection.

Compliance to prescribed palivizumab was calculated based on the number of doses received versus the expected number of doses for each participant. The expected number of doses for each participant was estimated based on seasonality and current prescription guidelines for each country.

The percentage of participants with each and combinations of the three comorbidities for which palivizumab is indicated.