When there is a disease outbreak, traditional vaccines and public health messages may no longer be enough to provide sufficient protection. In an essay that appears today in the journal Science, Dr. Alison P. Galvani, professor at the Yale School of Public Health, contends that social contagions, the beliefs or impressions that are quickly passed from person to person via social media, the influence of popular cultural figures or from other sources, pose a unique set of scientific and public health challenges.