A recent attempt at a dengue vaccine faced a similar problem. The most dangerous kind of dengue fever happens when you are infected a second time, by a differen

A recent attempt at a dengue vaccine faced a similar problem. The most dangerous kind of dengue fever happens when you are infected a second time, by a different variant than you were infected the first time. It turns out that the vaccine ended up having a similar effect as catching dengue for the first time. People who never had dengue and got vaccinated had a lower chance of catching the disease in the future. But if they did catch it there was a higher risk of it being the more dangerous version. The end result is that the vaccine is now only recommended for people who already had dengue before. https://en.wikipedia.org/wiki/Dengvaxia https://en.wikipedia.org/wiki/Dengvaxia