Electron microscope image of the bacterium (Bordetella pertussis) responsible for pertussis (whooping cough).
Image: Sanofi Pasteur via Flickr, CC BY-NC-ND 2.0
Cases of whooping cough dropped precipitously after introduction of the vaccine in the 1940s. The disease has been on the rise since health officials replaced the old vaccine with a newer version with fewer side effects. (Source: CDC)