Successful campaigns to combat the COVID-19 pandemic depend, in part, on people's willingness to be vaccinated. It is therefore critical to understand the factors that determine people's vaccination intentions. We applied a reasoned action approach - the theory of planned behavior - to explore these factors. We used data from an online survey of adults (18-74 years; n = 5044) conducted in Germany between April 9 and April 28, 2021 and found that attitudes toward getting vaccinated predicted vaccination intentions, while normative and control beliefs did not. In turn, positive attitudes toward getting vaccinated were supported by trust in science and fear of COVID-19 whereas negative attitudes were associated with acceptance of conspiracy theories and skepticism regarding vaccines in general. We advise policymakers, physicians, and health care providers to address vaccination hesitancy by emphasizing factors that support positive attitudes toward getting vaccinated, such as prevention of serious illness, death, and long-term health detriments, as opposed to exerting social pressure or pointing to the ease of getting vaccinated.