Vaccines, like the Corona Virus Disease-2019 (COVID-19) vaccines, can control diseases, but vaccine hesitancy reduces their use. It is important to assess the intention to use COVID-19 vaccines boosters and the determinants of this intention to help in developing programs to promote the uptake of boosters. An online survey collected data from adults in Egypt between March and June 2022 using a questionnaire that assessed demographic characteristics, and constructs of the Theory of Planned Behaviour (TPB) and the Health Belief Model (HBM). The survey was uploaded to SurveyMonkey and the links were posted on social media platforms. Binary regression analysis was used and the dependent variable was intention to use boosters of COVID-19 vaccines. The independent variables were indicators of the HBM including perceived susceptibility to COVID-19 infection (medical history) and possibility of disease prevention (awareness of the availability of types of COVID-19 vaccines); and indicators of the TPB including attitude toward COVID-19 vaccines (that they are harmful, that they may lead to death and confidence in locally and foreign manufactured vaccines), perceived norms (the percentage of vaccinated persons in one's circle) and perceived control over booster uptake (presence of government mandates for COVID-19 vaccination). The confounders were sociodemographic factors (age, sex, education, and place of residence). Complete responses were available from 1113 out of 1401 participants (79.4%), with mean (SD) age = 25 (9.5) years, of whom, 66.7% (n = 742) were females and 68.6% (n = 764) were university students. About 39.4% and 31.2% indicated that they would get or would definitely get the booster dose of the COVID-19 vaccines. In multiple regression, intention to use a booster dose was significantly related to not agreeing (AOR = 4.87, P < 0.001) or not agreeing at all (AOR = 8.46, P = 0.001) that vaccines are harmful and to having no confidence (AOR = 0.21, P < 0.001) or no confidence at all (AOR = 0.14, P < 0.001) in foreign-manufactured vaccines. Most university-educated Egyptians in the study intended to take the COVID-19 vaccine booster dose and this intention was associated with attitude toward the harm of the vaccine and confidence in foreign-manufactured vaccines. Awareness campaigns are needed to counteract misinformation and promote booster dose uptake.