This did not really happen. Cows' heads did not emerge from the bodies of people newly inoculated against smallpox. But fear of the vaccine was so widespread that it prompted British satirist James Gillray to create this spoof in 1802. H. Humphrey/Henry Barton Jacobs Collection, Institute of the History of Medicine, JHU hide caption

itoggle caption H. Humphrey/Henry Barton Jacobs Collection, Institute of the History of Medicine, JHU

Vikram is the first child to wear a Khushi Baby necklace, which will keep track of his immunizations. He's at a vaccine clinic in Rajasthan, India. Ruchit Nagar/Courtesy of Khushi Baby hide caption

itoggle caption Ruchit Nagar/Courtesy of Khushi Baby

Proteins and enzymes that will produce antibodies for the experimental Ebola drug ZMapp are developed on the leaves of the nicotiana benthamiana plant, a relative of tobacco. Here, indicator proteins glow under ultraviolet light — a way to assess the success of bacteria spread. Sean Gallup/Getty Images hide caption

itoggle caption Sean Gallup/Getty Images