Background: The length of hospital stays for severe COVID-19 cases significantly impacts the overall burden on the health system. Current COVID-19 vaccines have proven effective at reducing severe cases. However, the influence of vaccination status on the progression of COVID-19 after hospitalization is not well understood. Here, we estimated the impact of vaccination on the length of stay of hospitalized COVID-19 cases in Brazil. Methods: We utilized nationwide data from hospital stays due to COVID-19 and the vaccination status of over 1.6 million individuals who tested positive for COVID-19 between January 17, 2021, and January 31, 2022. A competing-risk survival analysis was conducted to assess the COVID-19 in-hospital progression. We considered the hospital pathway according to four states: ward, ICU, discharge and death and measuring the length of stay accordingly. Findings: Over half of hospital patients were unvaccinated. For patients aged 50-69-year-olds, the average length of stay for those discharged directly from the hospital ward (ward-to-discharge) ranged from 12.51 days (95 % CI, 12.39-12.63) in the unvaccinated to 11.02 days (95 % CI, 10.98-11.07) in booster recipients. Similar results were observed in the 20-49 and 70 or + age groups. For all age groups, the average time between hospital admission and ICU entrance was shorter in the unvaccinated. In the 50-69 age group, the average interval between ICU and discharge was 19.29 days (95 % CI, 18.95-19.64) in the unvaccinated and 16.92 days (95 % CI, 16.78-17.07) in the booster recipients, with a similar trend in other age groups. A higher discharge probability was observed among vaccinated individuals including hospital-to-discharge and ICU-to-discharge pathways. Interpretation: Vaccination reduced hospital admissions and length-of-stay across the hospital-to-discharge and ICU-to-discharge pathways, contributing to a reduced health system burden. Our results demonstrate that even when vaccines do not prevent severe cases leading to hospitalizations, they significantly shorten the duration of hospital stays.