There are a large number of fundamentalist right-wingers in this country who have declared war on science, and unfortunately, too many GOP congress people are in that number. They are unhappy because science sometimes disagrees with their "holy" books, so they have decided that science must be wrong. Their efforts to denigrate science has resulted in them attacking a variety of different scientific fields (including biology, physics, astronomy, climatology, geology, etc.).
And the field of medicine has not been immune to this threat from the right. There is a fairly large sub-group of these anti-science people known as "anti-vaxxers". These people would have you believe that vaccines are a bad thing. They now refuse to allow their children to get vaccines that have been proven effective, and they encourage other to do the same (using fallacious claims and junk science).
The chart above is from Forbes Magazine, and was compiled from information available from the Center for Disease Control. It shows just how valuable vaccines have been to the American population -- by eliminating some diseases and severely reducing the incidence of many others. These are diseases that once posed a serious risk to both children and adults in this country, but thanks to vaccinations they no longer are a danger to most.
Frankly, I do not understand the idiotic position taken by those opposed to vaccines. Do they want us to return to a time when all of these diseases ravaged our country? Because that is what their beliefs would do if followed by a significant portion of the population. This is inexcusable. We have come a long way since the time when nothing much could be done to fight disease, and much of that progress is due to vaccines. It would be insane to go backwards now, and let these diseases once again take hold.