This study is testing a new COVID-19 oral vaccine, called **VXA-CoV2-3.3**, against the currently approved COVID-19 booster shots. It aims to see if this new tablet form works as well as the shots. The study targets adults who have already completed their initial COVID-19 vaccination series and have not received a booster in the last 6 months. Participants will be monitored for their response to the new vaccine. **Key Points:** - Participants must attend all study visits and comply with requirements, such as not taking certain medications or participating in other trials during the study. - The study will include medical evaluations to ensure that participants are healthy enough to participate. - There is a commitment to use effective contraception and refrain from donation activities during the study. This study is important because it could lead to an easier way to protect people from COVID-19, by using a tablet instead of a shot. Participants should consider their health status and willingness to follow study guidelines before joining.