Hepatitis C was not mentioned because Imagine's question was about immunisation and there is NO vaccine for hepatitis C, which is a serious worldwide liver disease.
Medical expenses may not be paid by insurance companies for claims resulting from a tropical or other disease where you have not had the recommended vaccinations and / or taken the recommended medication.
It's entirely up to members whether they bother with "this health stuff" or even insurance. They're free to make up their own minds.