Early Detection, Rapid Response Key to Containing Global Flu Pandemic

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Avian Flu Response

Combining the time-honored public health measures of early detection, contact tracing, and quarantine, along with the rapid distribution of 100,000 to 1 million courses of antiviral medication, may be able to nip a threatened global pandemic of avian flu in the bud. So say mathematical models developed by Ira Longini, PhD, and Elizabeth Halloran, MD, DSc, professors of biostatistics in Emory University's Rollins School of Public Health, along with colleagues from Emory, the Johns Hopkins University Bloomberg School of Public Health and the Ministry of Public Health in Thailand. Their findings are published in the August 2005 issue of the journal "Science."

The researchers defined successful containment as fewer than one in 1000 people becoming ill with the new strain of influenza. They determined that the response must be rapid. Health officials would be most likely to contain an outbreak within a community if they were able to respond with quarantine and geographically targeted use of antiviral medication within 14 days of when the first infected person in the community becomes symptomatic.

The researchers believe the World Health Organization’≥ current stockpile of 120,000 courses of antivirals would probably be sufficient to contain an outbreak if it remained localized. If there are several different major centers of infection, however, up to 1 million courses of medication may be required, they say.

For the last several years, public health officials have been preparing for the possibility of a global flu pandemic, and they predict the virus would first appear in Southeast Asia as a mutation of an avian variety of influenza. The research team used sophisticated mathematical models to predict how the new virus might spread throughout rural villages in South East Asia, and simulated a variety of possible responses by the public health community. Their results provide a foundation for public health officials who have the daunting task of planning a response to an emerging infection that they have never before faced.

While public health officials have historically responded to influenza pandemics through isolation and quarantine of exposed individuals, new pharmaceuticals could help contain a new influenza strain. Dr. Longini predicts that, when a new case is found, treating a community with antiviral medications could greatly reduce the chances of the disease spreading to other parts of the world. The possibility of pre-vaccination with new influenza vaccine could also play a role in containing an emerging virus.

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"Even if a vaccine is developed that only provides immunity in half of the population, it could play a major role in containing a new or mutated strain of the influenza virus if the population is pre-vaccinated," says Dr. Longini.

When public health officials prepare to respond to a potential influenza pandemic, they study pandemics that the world has faced before. However, a strict examination cannot take into account the dramatic change in world's migration and travel habits. Dr. Longini's models were based on several population and migration studies of residents of rural South East Asia. They used those numbers to examine a number of infection patterns among 500,000 people spread through different geographic pockets across the region. They were then able to estimate a variety of possible rates and patterns of infection.

While their mathematical models took into account a number of variables in population and possible influenza strain, the authors warn that it is impossible to account for all possible variables when trying to predict how a new strain of influenza would behave.

"It is important to remember that these models represent possible outcomes," explains Dr. Halloran. "We expect that the situation will continue to evolve. As it does, we will continue to change our variables, and provide new intervention strategies for an emergent strain of influenza."

This is not the first time that Dr. Longini and Dr. Halloran have used this type of mathematical modeling to examine possible response strategies to infectious disease threats. In 2004, they used similar modeling to study how the U.S. could better use the limited vaccine supply to minimize the impact of the annual flu season in the U.S. Soon after the 9/11 terrorist attacks, they used a mathematical model to examine a number of possible strategies to contain a smallpox bioterrorism attack.

Their latest study on containing pandemic influenza was supported by the Models for Infectious Disease Agent Study (MIDAS) network of the National Institute of General Medical Sciences (NIGMS), NIH. Other co-authors of the study include Azhar Nizam, MS, and Shufu Xu, MS, of Emory's Rollins School of Public Health, Kumnuan Ungchusak, MD, and Wanna Hanshaoworakul, MD, of Thailand's Ministry of Public Health, and Derek A. T. Cummings, PhD, with the Johns Hopkins University Bloomberg School of Public Health. - Atlanta

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