Mass Vaccination May Be Best Response to Smallpox Attack Say Yale School of Management and M.I.T. Sloan Experts

New Haven, CT, July 3, 2002 - In the event of a smallpox attack, a mass vaccination policy would result in fewer deaths and faster disease eradication than alternative vaccination strategies, reports a new study published in Proceedings of the National Academy of Sciences (article 2827). Since the terrorist attacks of September 11, the best response to a smallpox attack has been a topic of hot debate.

Yale School of Management expert Edward Kaplan, the William N. and Marie A. Beach Professor of Management Sciences & Professor of Public Health, and colleagues from M.I.T.'s Sloan School and Operations Research Center, used a mathematical model to compare a number of different vaccination strategies on disease spread and death resulting from a smallpox attack on a large urban center.

The Centers for Disease Control and Prevention's (CDC) current response plan, endorsed by the Advisory Committee on Immunization Practices on June 20 calls for isolation of confirmed smallpox cases and targeted vaccination of only those who have been in contact with infected individuals, with a mass vaccination effort to take place only if the initial vaccination and quarantine methods are unsuccessful. Parameters of this new mathematical model include the number of people initially infected, the transmission rate, the fraction of potential contacts named by infected individuals, and the resources available to track potential contacts and administer vaccinations.

Under several different scenarios, the model predicted that mass vaccination would stop the spread of infection faster and result in fewer deaths than targeted vaccination or the CDC plan. In fact, the currently endorsed plan led to an estimated 4,120 additional deaths compared to a mass vaccination plan implemented from the beginning in a large attack on a city with 10 million inhabitants. The researchers found that a pre-attack vaccination of a portion of the population lessened the gap between the different strategies. These results suggest that unless a pre-attack vaccination is used to increase immunity within the population, a mass vaccination strategy should be seriously considered.

Media contact: Edward H. Kaplan, Yale University School of Management, and the Department of Epidemiology and Public Health, Yale University School of Medicine, New Haven, CT; tel. (203) 432-6010, fax (203) 432-9992.