Conventionally, Disease is the symptoms you get. And the symptoms you get, like fever, are often the symptoms of your immune reaction to the infection.
In the case of Dengue, there are a couple of related, co-existing Dengue viruses. When you get infected, you get an immunity which protects against that type, but is reactive to all types.
So later, when you get your second Dengue infection, you get a strong immune response, and disease, which is not effective against the virus. So you are getting the fever, and you still have Dengue, and you are getting more fever, and you still have Dengue.
Influenza is also a disease which is described by it’s symptoms. If you get intestinal influenza, they probably aren’t going to call it ‘flu’. If you get ‘flu’ and die of subsequent bacterial pneumonia, you’ll probably be counted as a ‘flu’ fatality. You get the same immune response from the flu vaccine: that’s how it works. Fortunately, the immune response to the flu vaccine is small and self limiting: there is no actual infection, no actual influenza, nothing to maintain an extended and dangerous “disease”. But if you are unlucky, and the vaccine manufacture is unlucky you do get some flu from the flu vaccine.
For this reason, flu vaccine is a matter of choice for most people. It’s considered important for old people, but for the rest, it’s something you do because you don’t want the flu, or because you live or work with old or compromised people.
So it is entirely reasonable for a fit married 30yr old, no parents, no children, good health insurance, somebody to care for you if you are sick, to decide not to bother with the flu vaccine every year. The pain is yours, the benefits mostly somebody else’s.
Of course, having said that, the OP describes a situation where they got infected before vaccination, and got sick after vaccination.
Personally, I don’t eat yogurt. I got sick with a sore throat in 1975, fpr twp days ate sweet yogurt because it soothed the throat, then was sick as a dog with influenza for the next 10 days. I really didn’t like having the flu. I get vaccinated, and I avoid yogurt. You might think those two actions are not equally effective, but the emotion is real.