That's a non-starter. You can't even use women in most clinical trials, because they might get pregnant. Clinical trial selection is actually a huge methodological rabbit hole, if you want to get into some really concerning weeds.

There are other experimental designs that could be used, though. One is what's called "Intent to Treat" where one group is given an extra reminder to keep up with the vaccine schedule. Then you use the difference in compliance rates to evaluate the schedule.