Some Vaccines Support Evolution of More-Virulent Viruses (image) Penn State Share Print E-Mail Caption This image shows chickens in agricultural production. Credit Andrew Read, Penn State University Usage Restrictions The image credit must be published along with the image. Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.