The H1N1 Swine Flu Pandemic of 2009-2010 Resulted in the Immunization

The H1N1 swine flu pandemic of 2009-2010 resulted in the immunization of millions of people.When the immunizations were first available,people under 25 or over 65 were given priority.This was done because H1N1

A) was a hazard to people in these age groups,and only these people were vulnerable to infection.
B) these age groups were most vulnerable to the hazard,putting them at greatest risk.
C) was not a hazard to these people,but they were most vulnerable to infection.
D) vaccines only worked on people in these age groups.