Human Influenza: Seasonal Outbreaks and Unpredictable Pandemics

During the winter season, influenza strains are transmitted rapidly among human beings and cause major illness and death. It is estimated that between 3,000 and 49,000 people in the U.S. die from seasonal influenza every year.1 The influenza strains that cause seasonal outbreaks continually evolve as they circulate among human populations and can acquire decreased or increased virulence. Pandemic outbreaks, in contrast, originate with an animal-adapted strain. They occur when a human-adapted strain receives a new “HA” gene from an animal-adapted strain or when an entire animal-adapted strain becomes adapted to humans.

Four influenza pandemics have been observed in the past 100 years: “Spanish” flu (H1N1) in 1918, “Hong Kong” flu (H3N2) in 1968, “Asian” flu (H2N2) in 1957, and “swine” flu (H1N1) in 2009. In the intervening years, these four strains have circulated as seasonal flu and “mixed” with other animal-adapted strains to form new variants.


Dr. Taubenberger discussed his research on the Spanish influenza outbreak of 1918, and Dr. Webster discussed past and recent developments in H5N1 research. Drs. Taubenberger and Webster addressed a number of questions, including: What was the scientific rationale for undertaking the research? What security and safety risks were considered prior to beginning the research? How, and by which individuals or entities other than the researchers themselves, were these risks weighed, and what kinds of precautionary or counter-measures were mandated or considered? Was the process for the risk-benefit assessment prior to the research optimal, and what might have been done differently? Why has the reaction to the H5N1 research played out differently from other dual-use research? What is different or distinct about the science, design and conduct of research, policy implications, or governance of the H5N1 research as opposed to earlier work such as the reconstruction of the 1918 Spanish Flu virus? What lessons can we learn regarding the design, conduct, communication, and oversight of future life sciences research of concern? Is there scientific research where the risks of undertaking the research outweigh the benefits of undertaking the research, and who or what institutional or societal processes are or should be in place to make such determinations?


1 Centers for Disease Control and Prevention, “Estimating Seasonal Influenza-Associated Deaths in the United States: CDC Study Confirms Variability of Flu,” June 24, 2011,

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