Background: Pneumonia is a leading cause of mortality in children. Despite more than 50% of pneumonias are due to viruses, because it is difficult to rule out bacterial etiology, initial management of pneumonia in children usually includes antibiotics, often unnecessary. In 2006 was designed and validated a clinical prediction rule (BPS: Bacterial Pneumonia Score) which accurately identifies hospitalized children's risk of bacterial pneumonia. Recently, we assessed BPS efficacy on reducing antibiotic use by 50% in children with CAP, in an ambulatory setting. However, BPS was tested in children not vaccinated against S. pneumoniae.