Not necessarily. Everyone gets sick, but not everyone responds the same way to the same meds. They may work for most but not all. Still, the person it doesn't work for can be sick with the same bug that the others had who did respond.
I don't know if that makes sense. Some diabetics respond best to natural insulin. Some respond better to synthetic and some do best with dietary changes. Some need all three. They are all diabetic. Its the same with anything. Some people just react differently due to body chemistry and the way their bodies handle the med.