The science behind preparing and responding to pandemic influenza: the lessons and limits of science.

A strong evidence base provides the foundation for planning and response strategies. Investments in pandemic preparedness included support for research that aided early detection, response, and control of the 2009 influenza A (H1N1) (pH1N1) pandemic. Scientific investigations conducted during the pandemic guided understanding of the virus, disease severity, and epidemiologic risk factors. Field investigations also produced information that strengthened guidance for the use of antivirals, identification of target populations for monovalent pH1N1 vaccine, and refinement of recommendations for social distancing measures. Communication of this evolving evidence base was important to sustaining credibility of public health. Areas where substantial controversy emerged, such as the optimal approach to respiratory protection of healthcare workers, often suffered from gaps in the evidence base. Many aspects of the 2009-2010 pandemic influenza experience provide ongoing opportunities for additional study, which will strengthen plans for future pandemic response as well as control of seasonal influenza.