More Science Why Haven't We Found an AIDS Vaccine? Jon Cohen argues that the obstacles may be more human than viral By Nancy Padian THIS ARTICLE IS ONLY AVAILABLE AS A PDF. Buy this digital issue or subscribe to access the full article. Already a subscriber or purchased this issue? Sign In Buy Digital Issue $7.99 Add To Cart Print + DigitalAll Access $99.99 Subscribe ADVERTISEMENT Scientific American is a trademark of Scientific American, Inc., used with permission © 2015 Scientific American, a Division of Nature America, Inc. All Rights Reserved.