Healthy adults and older children often get the flu, it's just that they're better able to fight it off. The H1N1 flu that circulated in 2009-2010 was particularly notable for hitting the younger, healthier population.
Okay yeah, healthy people can still get sick, but if you're young and healthy, then you can fight it off better. Saying that the vaccine works best for healthy people, the same ones who would naturally be better at fighting it off in the first place, sounds more like an argument against the vaccination, not for it.
If I'm young and healthy, there's less need for me to get the vaccine because even if I get the flu, I can fight it off. Saying the vaccine works better for me because I'm young and healthy seems redundant or irrelevant or something. It gives me even less chance of getting something I was going to be better at fighting off in the first place.
The fringe groups, older folks and young children, the ones with weaker immune systems in general, are also less likely to benefit from the vaccine.
I'm sorry, but it still sounds like you're not getting a lot of benefit from the vaccine. It's less effective for the very people you want to protect most, and more effective for the ones who can already fight the flu better.
Technically, anything resulting from contaminated food is food poisoning (although I think the actual term is "foodborne illness"); usually these are viruses or bacteria. How severe it is just depends on which particular nasty is in your food.
https://en.wikipedia.org/wiki/Food_poisoning
That's what I figured, but it just seems to me that the same term shouldn't be used to define both moldy bread and soup laced with arsenic. "Foodbourne illness" at least has a more general sound to it, though I don't know if that's any better, and "poison" to me conjures up something intentional and usually synthetic. But maybe that's just me.