I have had a look at several websites, and Aspartame is not listed on the ingredients of this particular vaccine, so it is interesting that this particular website warns people who are allergic to Aspartame to not have the oral vaccine. I'll check this out with my friend, an immunologist, and see if she can shed any light on this, she has access to a lot more information than I do. I'll post any info I find.
Even if this oral vaccine contains a minute amount of aspartame, IMO it is unlikely to pose any real danger, (unless of course the person is allergic), as the amount of Aspartame adults would ingest if they drink diet drinks or eat food with artificial sweeteners added, would be vastly more than a single dose oral vaccine.
If you don't want to ingest aspartame, then don't drink any diet soft drinks, or eat any diet food that contains artificial sweeteners.