[dudeofea]

Dengue. The initial vaccine did not target all subtypes of dengue, causing "severe dengue" in infections after a naive individual was vaccinated. The same could happen if someone moved from one region to another, since the subtypes inhabit different regions. Your body will respond to one subtype's antigens primarily with it's initial conditioning. If you weren't conditioned with that subtype, you get original antigenic sin / severe dengue

https://www.cdc.gov/dengue/prevention/dengue-vaccine.html

The worst-case scenario for a vaccine is not "no immunity", it is negative immunity. If your adaptive immune response outcompetes your innate immune response in binding to antigens, but does not neutralize them, then your immune system will struggle to fight off an infection