What do Mrs Johnson's cold hands indicate?

It depends on the numbers, of people who were in the area. for you can not determine those who suffered minor injuries, without more information.

A. fewer job oppurtunities for the mother

Immunization is the introduction of a foreign substance to provoke  the immune response system.  immunizations are the same as vaccinations. it introduces foreign (but dead/ weakened) illnesses to train the body to fight against them. specific viruses and bacteria have specific antigens, antigens act sort of like name tags. these name tags the immune system recognize what's dangerous to the body and what's safe.