What makes a particular strain of the flu more aggressive than others? Is there a disease model that can explain why the severity of flu seasons can vary? A study published in October 2006 in the online journal Biology Direct, researchers suggest that one possible avenue to explain these variations is an ongoing competition between different strains of flu virus each trying to outdo the other with respect to their ability to infect humans.

• Dr. David Lipman, Director of the National Center for Biotechnology Information (NCBI), which is a division of the National Library of Medicine within the National Institutes of Health and senior author of the study