To analyse the completeness of the COVID-19 vaccination schedule and identify factors associated with vaccine uptake.

Cross-sectional study.

Data were collected through face-to-face interviews conducted in all 26 Brazilian state capitals and the Federal District between 2022 and 2023, using a sequential sampling approach.

A total of 1392 individuals aged 18 years or older experiencing homelessness for at least 6 months were included.

The primary outcome was the completeness of the COVID-19 vaccination schedule (complete vs incomplete), based on self-reported vaccination status. Secondary analyses examined sociodemographic, institutional and behavioural factors associated with vaccine uptake using binary logistic regression.

Completion of the vaccination schedule was positively associated with receiving government aid (OR: 1.58; 95% CI 1.09 to 2.30), visits from street clinic health agents (OR: 3.19; 95% CI 1.95 to 5.36), prior COVID-19 diagnosis (OR: 5.77; 95% CI 3.17 to 11.15), support for mandatory vaccination (OR: 3.76; 95% CI 2.48 to 5.76), trust in vaccine efficacy (OR: 3.92; 95% CI 2.63 to 5.89), seeking information from community sources (OR: 1.91; 95% CI 1.01 to 3.88) and trust in federal authorities (OR: 1.57; 95% CI 1.06 to 2.31).

This study identified structural, social and individual factors associated with complete COVID-19 vaccination among people experiencing homelessness in Brazil. Although overall coverage was substantial, gaps in vaccination completeness persisted. Social support, healthcare outreach and trust in vaccines were associated with higher uptake, highlighting important barriers and facilitators to vaccination in socially vulnerable populations.