The CDC is the government organisation in charge of public health. For example if a contagious virus such as Ebola were to break out in America, they would be the ones working on a vaccine and a cure.
They also set the BMI scale I believe, which is an equation that tells you your weight conpared to your height and shows it in several ranges from underweight to morbidly obese.
The flu is spread every 30-45 years since the 16th century, so we know when to prepare and how to do it. Also, we have learned where it will strike and the containment. Hope this helps! :)
