Abstract Objective This study aimed to investigate factors influencing the uptake of first and second COVID-19 booster vaccines among adults in Belgium, particularly age, sex, region of residence and laboratory confirmed COVID-19 infection history. Results A binomial regression model was used with having received the first or second booster as outcome and age, sex, region of residence and infection history as fixed variables. Among adults, there was generally a higher uptake to receive the first booster among older age groups compared to younger ones. Females, individuals residing in Flanders and those with no previous COVID-19 infection were more likely to receive the first booster. For the second booster, the same age trend was seen as for the first booster. Males, individuals residing in Flanders and those who tested positive for COVID-19 once after first booster were more likely to receive the second booster. Individuals with multiple positive COVID-19 tests before and after primary course or first ...