Widespread Smallpox Vaccination Is Too Dangerous

January 2003

Widespread vaccination of Americans against smallpox is too dangerous to justify unless the likelihood of a major biological attack on the United States is substantial, but it is prudent to vaccinate health care workers now against the deadly disease, according to a new study by the RAND Center for Domestic and International Health Security.

The study, published on the Web site of the New England Journal of Medicine, estimates that if 60 percent of the U.S. population were immunized, there would be about 500 deaths — a price too high to pay if there is little chance of a widespread attack against America with the smallpox virus, researchers said.

The researchers found that if nearly all 10 million health care workers in the United States were vaccinated against smallpox, an estimated 25 people would die. However, the researchers believe that this risk is justified because health care workers are particularly vulnerable during smallpox outbreaks, since they come in close contact with the sick, often before the disease is recognized.

The study shows that health care workers, who make up about 3 percent of the population, could account for more than half of all smallpox cases under some scenarios. Vaccinating health care workers would also help preserve staffing of critical facilities, the study concludes.

Health care workers are defined as everyone coming into direct contact with sick people. This includes doctors, nurses, and others working in and around health care facilities, including paramedics, ambulance drivers and hospital security guards.

The report is the result of a detailed analysis by physicians, biological scientists, terrorism experts and others of six plausible smallpox attacks launched against the United States by terrorists or an enemy nation. In addition to RAND, the study team includes researchers from the Department of Veterans Affairs and the University of California, San Diego.

"Drafting a smallpox vaccination policy must balance the potential for saving lives against the likelihood of losing lives from the complications of the vaccine itself," said Dr. Samuel A. Bozzette, the study's lead author, who is an infectious disease specialist affiliated with the VA San Diego Healthcare System, UC San Diego and RAND. "Vaccinating health workers presents a modest risk and could pay many benefits. In contrast, a public vaccination campaign is certain to entail significant harm, so it should only be contemplated if the government concludes that the chances of a widespread attack are considerable."

Dr. Kenneth Shine, director of the RAND Center for Domestic and International Health Security and past president of the Institute of Medicine, said: "An appropriate national strategy for smallpox vaccination depends on assumptions about the probability and nature of an attack. Drawing on the best available scientific evidence, this study has provided a tool to guide policy."

The study is the most comprehensive analysis ever conducted of the possible consequences of an attack against the United States using smallpox as a weapon. The study, which compares the consequences of various smallpox attacks under different vaccination policies, was made available to government officials for use in assisting policy formulation while undergoing the peer-review necessary for scientific publication.

President Bush ordered smallpox vaccinations Dec. 13 for 500,000 members of the U.S. armed forces, and offered vaccinations to civilian health care and emergency workers. However, the President strongly recommended against smallpox vaccinations for the remainder of the population at this time. He said there is no evidence of an imminent smallpox attack against the United States. The RAND study did not address the question of vaccinations for members of the military.

Smallpox is a serious, contagious, and often fatal infectious disease. Currently, there is no specific treatment for smallpox, and the only prevention is vaccination. Smallpox outbreaks have occurred periodically for thousands of years, but the natural disease was eradicated after a successful worldwide campaign. The last case of smallpox in the United States was in 1949. The last naturally occurring case in the world was in Somalia in 1977.

Concern about a potential smallpox attack has been growing since the terrorist attacks of Sept. 11 last year, the anthrax attacks that followed several weeks later, and with the prospect of war with Iraq. There is fear that terrorists or a nation at war with the United States may have access to the smallpox virus, possibly from stores created by the former Soviet Union as part of its biological weapons program.

While it is effective against the disease, the smallpox vaccine is made with a live virus and can cause serious illness and even death among a small proportion of people who receive it. Those vaccinated also may infect people excluded from receiving the vaccine because they are vulnerable to serious complications. The excluded group includes pregnant women; babies younger than a year old; people with HIV or other immune disorders; and people with some types of cancer, organ transplants, or histories of skin problems like eczema.

To study the risks and benefits of smallpox vaccinations, the RAND researchers developed a number of feasible smallpox attack scenarios, comprehensively reviewed historical smallpox outbreaks, and developed a computer model that estimates the number of people who might be killed in each of the attacks under a number of policy options.

The scenarios that researchers considered were: a hoax, infection of a laboratory worker who then infects his children; suicide attackers who ride mass transit spreading the virus; virus sprayed into the ventilation system of an office building; and both a high-impact and a very high-impact simultaneous spread of the virus in multiple airport terminals.

Assuming that once the infections were discovered exposed individuals would be isolated and vaccinations would begin, researchers estimated there would be, on average, seven deaths in the laboratory incident, 19 in the transit attack, 300 in the building release, 2,735 in the first airport scenario, and 54,728 in the high-impact airport attack.

When researchers changed the model to include inoculating health care workers against smallpox before an attack, the number of deaths declined in the building and airport attacks, but deaths from the vaccine outweighed the benefit in other attacks. Vaccinating the general public provided a net benefit only in the attacks on multiple airports.

Bozzette and his colleagues urge that priority be given to developing improved methods of detecting and treating smallpox outbreaks. Early response requires investment in education, surveillance and response capabilities, they contend.

Other authors of the study are: Rob Boer of RAND and Erasmus University in the Netherlands; Vibha Bhatnagar of the VA San Diego Healthcare System and UC San Diego; Jennifer Brower, Emmett Keeler, Sally Morton and Michael Stoto, all of RAND.


The RAND Center for Domestic and International Health Security seeks to make health a key component of U.S. foreign policy, strengthen the preparedness and response of the U.S. health care system to terrorism, and prepare Americans to cope with the psychological effects of terrorism. It is part of RAND Health, one of the nation's leading health policy research organizations with a broad research portfolio that focuses on health care costs, medical quality and delivery of health care, among other topics.

The RAND study will be published in the Jan. 30 print edition of the New England Journal of Medicine. Journal editors decided to release the study sooner on the publication's Web site because of the reportís importance to the national debate over developing a national smallpox vaccine strategy.

The study was funded by RAND, with additional support from the Health Services Research and Development Service of the Department of Veterans Affairs.

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