This question involves vaccination and herd immunity.
Question A: Smallpox is a good choice for two reasons. First it is a dangerous pathogen which is easily spread from person to person. Secondly, there is very little herd immunity to it. Vaccination for smallpox was halted decades ago and is only seen in the military today. Therefore the size of the herd that is immune to smallpox is quite small making the number of potential targets for infection very high.
Question B: Obviously vaccination of the population would be the best protection because of the herd immunity factor. If the vaccination of the populace was complete, it would severely limit the infection possibilities and reduce the usefulness of smallpox as a weapon.
Question A: Millicent should be concerned because of her grandmother’s age, which we have seen, can be linked to a diminished immune capability. She is also in a home where the possibility of transmission is high. However her concerns are somewhat diminished because her grandmother has lived there for 6 years and though exposed to this infection did not become sick. Therefore she may have a very competent immune system that is defending her.
Question B: Millicent probably should not be concerned because she is young and therefore her immune system should be capable of defending her. However, the fact that she knows there is a pneumonia problem in the home and she is visiting on a regular basis she might consider getting a vaccination against pneumonia.