Tom Frieden

New, unfamiliar, and mysterious threats to our health are scary. At the Centers for Disease Control and Prevention - where we identify, on average, one new health threat each year - we work around the clock with an approach that prioritizes finding out what we need to know as fast as we can to protect Americans.

Zika is spread by mosquitos. They are tough to control. It will bite four or five people at one blood meal. They can breed in the amount of water it takes to fill up a bottle cap or, theoretically, even a drop of water. You have to get rid of maybe 90% of them or more before you protect people.

States should require vaccinations for communicable diseases, like measles and the mumps. But you can't catch HPV if an infected schoolmate coughs on you or shares your juice box at lunch. Whether or not girls get vaccinated against HPV is a decision for parents and physicians, not state governments.