While it is true that immune system can ward off a lot of infection. Calling a person's immune system "strong" is something that is not accurate. Immune systems are just different for each person. While few individuals could be more resistant to certain infections. The same could be prone to other infections.
When it comes to dengue. We should remember that it affects enough number of people that it is an illness that can defeat most immune systems initially. How individuals react to the same virus is very nuanced and most people who contract the dengue hemorrhagic fever virus, fall sick.
Next Steps
knowing that dengue is a prevalent infection spread via mosquitos. it is imperative to keep our protective measures intact, as we do not know which infections are going to cause a serious illness.