Popa
Hep B is usually spread through blood or intimate contact but can be spread in the following ways as well:
Direct contact with infected or contaminated blood, even in tiny amounts too small to see
Sharing personal items, such as toothbrushes, razors, syringes, or glucose monitors that have even microscopic amounts of blood on them
Direct contact with open sores of an infected person
An infected mother passing it to her baby at birth
(from the cdc.gov)
The point is that diseases can be spread without you being aware of having definite blood contact with an infected person. To say that living in the frum world does not expose you to any diseases is incorrect.
As an example, if I, or any other healthcare professional, were not careful (and there are many healthcare professionals in the frum world), and would not be vaccinated, we can be a great transmitter of disease. Don’t think you live in a box and can avoid all vaccinations b/c the disease isn’t around.