Objective: To evaluate COVID-19 vaccination status in admitted children during the OMICRON variant circulation. Design: Observational retrospective study. Patients with confirmed COVID-19 were compared in two different periods: 2020-2021 when full COVID-19 vaccine were not completed for adolescents between 12 and 18 years and 2022, when Pfizer-BioNTech vaccine full scheme were completed for children older 12 years Setting: Two paediatric hospitals in Rio de Janeiro, city Patients: Children aged <18 years with confirmed COVID-19. Intervention: None Main outcome: Vaccination status for COVID-19 at the admission. Results: Three-hundred patients were admitted with confirmed COVID-19, being 240 in 2020-2021, and 60 in 2022. The distribution of patients according to the age-groups were: 0-2 years (33.3% in 2020-2021 and 53.4% in 2022), 2-5 years (21.7% in 2020-2021 and 10% in 2022), 5-11 years (29.2% in 2020-2021 and 28.3% in 2022) and 12-18 years (15.8% in 2020-2021 and 8.3% in 2022) ( p= 0.015). The median of lenght of stay was 6 days in 2020-2021 and 5 days in 2022 (p=0.036). We verified 6 deaths and in the first period of analysis and 1 death in the second one (p=0.777). Of 60 children admitted in 2022, fifty-eigth (96.7%) not received the full scheme of COVID-19 vaccine available Conclusions: We verified in a real world condition ability of Pfizer-BioNTech vaccine in avoid hospitalization in children older than 12 years