Who to Vaccinate when Flu Season Strikes (IMAGE) PLOS Caption People are wearing face masks to prevent and control acquisition and transmission of influenza during the 2009 H1N1 influenza pandemic. Credit Demet/Flickr, <a target="_blank"href="https://creativecommons.org/licenses/by/2.0/">CC-BY</a> Usage Restrictions All figures and photographic images will be published under a Creative Commons Attribution License (CCAL), which allows them to be freely used, distributed, and built upon as long as proper attribution is given. License Licensed content 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.