There doesn't have to be one cause, it can be a storm of causes, antibiotics, hygiene, moisture issues etc. It's not likely the vaccine as it stimulates an immune response, not immunosuppression. I would stay away from ointments that have water as an ingredient and use an anti fungal powder and keep the area DRY. That means after you shower, take a blow dryer and blow dry your scrotum on the hottest tolerable setting until it's dry and then put on the powder. Keep it DRY DRY DRY
Throwing any ointment that has H20 as an ingredient into your groin area just feeds the fungi. You don't feed bears because you don't want them at your door, and you don't feed fungi for the same reason. Keep em dry and powdered. Zeasorb AF powder is your friend, and if it doesn't work with blow dry hygiene, then call in the heavy artillery, which would be Diflucan. And see a dermatologist for these issues, not a PCP.