Boston, MA -- Containing an emerging bird flu pandemic at its source will probably only delay--not stop--the illness' spread because of likely multiple introductions of the pathogen, assert researchers from the Harvard School of Public Health (HSPH) and the University of Washington in a policy paper in PLoS Medicine. The paper will appear in the open access journal online on Feb. 20.

"If a single introduction of a pandemic-capable strain is likely to happen, then multiple introductions are also likely," said HSPH Associate Professor of Epidemiology Marc Lipsitch. "If there are multiple introductions, then there are numerous chances for containment, and the strategy only has to fail once to result in a pandemic."

Containment describes attempts to reach a pandemic source as early as possible and then apply public health tools such as vaccination (if available), antiviral drugs, and quarantine to curb a pathogen's spread. Containment is one component of federal and World Health Organization planning for a possible flu pandemic.

The researchers argue that resources would be strained with each new effort at containment, making subsequent control strategies more and more difficult to implement. Under good circumstances, containment efforts may only double the time before a pandemic emerges, the researchers have calculated. That time could drop even further if efforts underpinning the containment, such as surveillance for human cases, are inadequate.

"From the point of view of policy planning, we should not give up on containment, but embed it within a multi-pronged plan that includes vaccine development, improved surveillance, and risk reduction measures, such as limiting human-to-bird contact -- particularly after the first containment effort," said lead author Christina Mills, doctoral student in the HSPH Department of Epidemiology.

Added Lipsitch, "Planning and investment should begin immediately to develop a multidimensional approach to maximize a containment strategy and reduce the devastating effects of a flu pandemic."

This work is part of the Models of Infectious Disease Agent Study (MIDAS) aimed at developing modeling techniques to understand the spread of infectious diseases, including pandemic flu, and the impact of various interventions. MIDAS is supported by the National Institute of General Medical Sciences (NIGMS) of the National Institutes of Health (NIH). Funding was also provided by the Ellison Medical Foundation New Scholars in Infectious Disease Program, the Medical Scientist Training Program Fellowship, the National Defense Science and Engineering Graduate Fellowship, NIH, and the National Institute of

Allergy and Infectious Diseases.

"Dr. Lipsitch and his research team demonstrate the power of mathematical analysis to give us insights into how pandemic influenza may spread and the effectiveness of containment strategies," said Jeremy M. Berg, Director of NIGMS, which partially funded the research. "The work also shows the value of continuing collaboration among mathematicians, modelers, and public health experts who are developing plans to protect the public from a pandemic threat."

Mills and Lipsitch were part of a team that published an analysis of the 1918 flu pandemic in Nature in December 2004. For more information on that paper, see here.