BACKGROUND: Acute respiratory infection (ARI) is the most frequent reason for children being seen by doctors worldwide. We aimed to estimate the frequency of complications in children aged 6-23 months during ARI episode and to evaluate risk factors present on recruitment associated with complications after the universal implementation of pneumococcal vaccine (PCV10) in our region. METHODS: This prospective cohort enrolled children who had shown ARI for up to 7 days and who were subsequently followed up 14-21 days after, in Salvador, Brazil. Data on recruitment were registered. The vaccine card was personally checked. Complication was defined when hospitalization, pneumonia or acute otitis media (AOM) were informed during the follow-up visit. Pneumonia and AOM were diagnosed by a doctor. Multiple logistic regression analysis was performed. RESULTS: Of 576 children, 422 (73%) returned and 79 (19%; 95%CI: 15-23%) had complications. The mean interval between admission and follow-up was 23±13 days. Pneumonia (n=47; 11%), hospitalization (n=28; 7%), and AOM (n=17; 4%) were reported. Most of the patients presented one complication (n=66; 84%) followed by two (n=13; 16%). Report of fever (92% versus 79%; OR [95%CI]: 2.90 [1.18-7.14]), bird at home (24% versus 14%; OR [95%CI]: 2.13 [1.07-4.26]), ronchi (48% versus 36%; OR [95%CI]: 2.06 [1.16-3.67]) or crackles (17% versus 7%; OR [95%CI]: 2.36 [1.04-5.38]) on auscultation were directly associated with complications whereas PCV10 (59% versus 75%; OR [95%CI]: 0.46 [0.26-0.82]) was inversely associated. Bird at home (OR [95%CI]: 5.80 [1.73-19.38]) and ronchi (OR [95%CI]: 6.39 [1.96-20.85]) were associated with AOM; PCV10 was inversely associated with AOM (OR [95%CI]: 0.16 [0.05-0.52]). Crackles were associated with pneumonia (OR [95%CI]: 2.55 [1.01-6.40]). CONCLUSIONS: One fifth of the children presented complications. PCV10 was independently associated with lower odds of development of AOM. Bird at home and ronchi are risk factors of otitis. Crackles are associated with pneumonia.