Hi Jessica, Because you mentioned earlier that there is a lot of mistrust about participating in vaccine trials among the population you are targeting, I suggest that you focus more on the perceived susceptibility, threat and barriers to participating (predisposing factors). Risk perception will be important, as will their expectations about the outcomes of participating in a trial. This is the precontemplation stage, and so you want to keep the movement forward.
Another predisposing/know topic: informed consent and voluntary participation?
As Lindsay stated, hearing others' stories of successful participation in vaccine trials (or resolution of unsuccessful participation) would be a great way to reinforce the reasons to join a study. Maybe under reinforcing/"reminded" you could include a phone call f/u to answer questions about the videos, or an email survey about the video and to gauge their interest in future studies?