Friday, April 22, 2005

New Study Evaluates Cost-Effectiveness of Defending against Anthrax Bioterrorism
By Julie McKeel

In a study analyzing the costs and benefits of postattack and preattack strategies for a large-scale bioterror release of Bacillus anthracis (anthrax), researchers found that the use of vaccine plus preventive antibiotic is the most effective and least expensive treatment plan in responding to an attack. The savings associated with preventing illness as a result of inhaling anthrax offset the cost of using both vaccination and antibiotics. The overall health benefit and cost-effectiveness of a preattack vaccination depended on the probability of an attack and on the proportion of the population exposed during the attack.

According to the investigators, the findings highlight the debate surrounding an anthrax vaccination policy. Several factors influence the probability that an individual will receive a life-threatening exposure during an attack, including the quantity of spores released, the distribution method, and the environmental factors (such as geography, wind conditions, and time of day of the attack).

Anthrax is one of the few biological agents identified by the Centers for Diseases Control and Prevention (CDC) as being capable of causing death and disease in large enough numbers to devastate cities or developed areas. The use of anthrax as a weapon has been researched since the 1920’s, and several nations are suspected of developing anthrax for this use. According to a World Health Organization estimate, the release (via aircraft) of 50 kg of anthrax over a city of 5 million people would result in 250,000 deaths, with 100,000 patients dying before receiving treatment.

The first of 22 cases of bioterrorism-related anthrax were identified in the United States in September 2001. Five people died by this exposure. Of the cases reported, 11 patients had inhaled the anthrax spores, and 11 more were exposed after handling the spores. The more than 10, 000 persons potentially exposed to anthrax in the U.S. were advised to take preventive antibiotics after the exposure. If inhaled anthrax is left untreated, the death rate is nearly 100%, and the costs associated with a real or perceived anthrax attack have been estimated at more than $26 billion per 100,000 persons exposed, according to the study authors.

The U.S. Department of Defense has now given more than 2 million anthrax vaccinations to more than 500,000 military personnel. This vaccination program includes an ongoing system that reports side effects and complications. The U.S. military has decided that the risk exposure justifies the costs and potential side effects associated with the vaccine, but a preventive vaccination policy for the civilian U.S. population remains controversial.

In this study, the researchers evaluated the cost-effectiveness of anthrax prevention and treatment strategies for cities at risk for bioterror attacks. They modeled a large-scale air release of anthrax over a U.S. metropolitan area, with the assumption that an air attack would guarantee a quick and wide-reaching exposure and thus strain the health care system’s ability to respond. They compared the costs, harms, and benefits of 4 postattack strategies (no vaccination, vaccination alone, preventive antibiotic alone, or vaccination plus preventive antibiotic) and 2 preattack strategies (vaccination versus no vaccination).

The authors set up the costs and benefits, discounted at 3% annually, following the recommendations of the Panel on Cost-Effectiveness in Health and Medicine. Medical cost estimates in the model included costs associated with preventive vaccination and antibiotic treatment, inpatient and outpatient medical care, potential lost earnings, death costs, and age-specific medical costs. The authors converted all costs to 2004 U.S. dollars by using the gross domestic product deflator.

Their model included people residing or working in a large U.S. city. Fifty-three percent of the people in this model were women, with a mean age of 36 years, and the life expectancy similar to those of New York City.

Based on the evidence presented in other studies about the possible side effects associated with the vaccine, the researchers assumed that 4% of the recipients may have minor vaccine-related side effects and that less than 1% may experience moderate or severe side effects.

The study results show that the use of the vaccine plus preventive antibiotic was the most effective and low-cost strategy. This combination strategy was less expensive because it prevented more cases of anthrax poisoning and more deaths than the individual strategies. The combination strategy also resulted in a slightly longer life span and a cost saving of $355 per person as compared with vaccination alone. The option of using no preventive vaccine or antibiotic was the least effective and most expensive strategy. Costs were higher without the vaccination or antibiotic because of the high cost of treating patients who had inhaled the anthrax spores. Relying on the vaccination alone after anthrax exposure was less effective than just the preventive antibiotic.

The study was funded by the University of Toronto and Sunnybrook and Women's College Health Sciences Centre, The Laughlin Fund, and the Agency for Healthcare Research and Quality.