The variable track record of past flu pandemics makes predicting the future course of 2009 H1N1 virus, which first emerged in the Northern Hemisphere in the spring of 2009, difficult. The authors contend that characteristics of the novel H1N1 virus, such as its modest transmission efficiency, and the possibility that some people have a degree of pre-existing immunity give cause to hope for a more indolent pandemic course and fewer deaths than in many past pandemics.

Still, the authors urge that the 2009 H1N1 virus continue to be closely tracked and studied as the usual influenza season in the Northern Hemisphere draws near. Like life, the authors conclude, paraphrasing Danish philosopher Soren Kierkegaard, "influenza epidemics are lived forward and understood backward." Thus, the robust, ongoing efforts to meet the return of 2009 H1N1 virus with vaccines and other measures are essential responses to a notoriously unpredictable virus.

DM Morens and JK Taubenberger. Understanding influenza backward. Journal of the American Medical Association 302: 679-80. DOI: 10.1001/jama.302.6.679 (2009).

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