*Modeling Influenza in Households*
By: Submitted by Lablover
14 December 2006

The committee first heard from Dr. Larry Wein, who presented an unpublished analysis to assess the effectiveness of nonpharmaceutical interventions during a severe influenza outbreak assuming: (1) no vaccine and a limited supply of antivirals, and (2) that most sick individuals would be cared for at home because hospitals would be too overwhelmed to treat all cases. His model was motivated by the observation that without an understanding of the likely route of transmission (i.e., aerosol, droplet, or contact), it would be difficult to understand how effective certain infection control measures, such as hand washing or face protection, would be in preventing transmission (Wein and Atkinson, 2006).

He estimated the probable route for influenza transmission using historical data on influenza and rhinovirus. He first formulated a simple model of transmission within a household. He then estimated various parameters necessary for his model for rhinovirustransmission, then extrapolated these findings to infer transmission of influenza. His review of the data suggested aerosol transmission as the primary form of transmission for influenza. The model also suggested that droplet transmission was an unlikely mode of transmission, and that contact transmission played a comparatively small role. He then extended this “in-household” model to a simple “between household” model to develop a“hierarchical epidemic model” (Wein and Atkinson, 2006).

His model predicts that short-range aerosol transmission would be the dominant mechanism of transmission for influenza, a finding that implies the importance of facemasks (specifically N95 respirators or modified surgical masks) and, to a lesser extent, room ventilation, humidifiers, and social distancing in reducing transmission. His findings further imply that hand washing would have little or no impact in limiting the spread of influenza infection.

Wein’s analysis sheds important light on blind spots in current thinking and raises questions about assumptions that were implicit in the other models presented. Specifically, his model highlights the significant uncertainty that surrounds the modes and mechanisms of influenza transmission, suggesting this as an important area for future study. In addition, Wein's analysis forces us to ask whether minimizing influenza transmissions is too narrow an objective, emphasizing the critical importance of further research to address these issues.

excerpt from:
Modeling Community Containment for Pandemic Influenza: A Letter Report
Submitted by Lablover

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