Vaccination plus antibiotics is best strategy to defend cities against bioterror attack

Researchers from Sunnybrook and Women’s College Health Sciences Centre suggest the most cost-effective method to defend against bioterrorism in a metropolitan area is timely access to preventative vaccination and antibiotics along with access to healthcare and infection control measures. Published in the April 19th issue of the Annals of Internal Medicine, researchers at Sunnybrook & Women’s join forces with researchers at Duke University, Stanford University, and the Department of Veterans Affairs (VA) Palo Alto Health Care System, to evaluate the cost-effectiveness of anthrax prevention and treatment strategies for urban centres at risk of a bioterrorism attack, by simulating a large-scale aerosolized release over a North American city such as New York or Toronto.

“An aerosolized release of anthrax could cause rapid and wide-spread exposure in a metropolitan population, placing a large burden on the health-care system,” says Dr. Robert Fowler, principal investigator and critical care physician at Sunnybrook & Women’s. “Although we hope and believe the risk of a bioterror attack is relatively low, our findings highlight the critical need for disaster planning which includes distribution systems that can be rapidly deployed to provide infection control, healthcare, antibiotics and preventative vaccinations for tens or hundreds of thousands of citizens.”

Anthrax is an acute infectious disease caused by the spore-forming bacterium Bacillus anthracis. It occurs more commonly in animals, but can occur in humans when they are exposed to infected animals or when anthrax spores are used as a bioterrorist weapon, as occurred with release within the US mail in 2001. Anthrax is one of few biological agents recognized by the Centre for Disease Control and Prevention (CDC) as capable of causing death and disease in sufficient numbers to devastate an urban setting.

To determine the most cost-effective method of defending against an anthrax attack, researchers looked at the costs, harms and benefits of four post-attack strategies Ñ no vaccination, vaccination alone, antibiotics, or vaccination and antibiotics Ñ and two pre-attack strategies: vaccination or no vaccination. By modeling an urban airborne anthrax attack and accounting for population density, size, height and wind dispersion of release, researchers determined the costs and harms for various rates of attack and exposure.

Assuming a low probability of attack, widespread preventive vaccination was more costly and less effective, due to the potential side effects of the vaccine. For a city of five million people, the incremental cost of such a prophylactic vaccination plan could be between $500 million and $1 billion, without appreciable health benefits. However, if an attack did occur, the combination of vaccination plus antibiotics is the optimal strategy, because it would prevent the most death and disease, and would cost less than any other strategy.

“The savings associated with preventing cases of inhalational anthrax offset the cost of using both vaccination and antibiotics,” says Dr. Fowler, who is also assistant professor in the department of medicine and interdepartmental division of critical care medicine at the University of Toronto. “The effectiveness of combination antibiotic and vaccination therapy after an attack may vary depending on the strain of anthrax employed, the timing of vaccination, and capability for mass health-care distribution systems.”

Fowler, who has an interest in economic evaluation of therapies for critical care stresses that the likelihood of a bioterror attach such as anthrax on an urban area is likely very small, but more planning needs to be done to prepare the healthcare system in an event of large infectious outbreaks or exposures. “The recent Severe Acute Respiratory Syndrome outbreak taught us that simulations and mock disaster exercises are paramount in preparing the healthcare system for rare but potentially crippling events – more work needs to be done.”

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