We need to make clear the connection between animal research and a grandmother's hip replacement, a father's bypass operation, a baby's vaccinations, and even a pet's shots.
Medical experts have said vaccinations and natural immunity in people who've been exposed to the disease are both playing a part in reducing America's cases.
Whereas in the past Australian parents could decline vaccination for their children based on a personal objection, now only a few medical or religious exceptions will be accepted.
That depends on both how widely it spreads around the world and the degree to which it erodes immunity – either that built up through infection or vaccination.
This can happen in one of two main ways either people recover from a disease and then become immune to it or an effective vaccination prevents people from getting sick.