Smallpox virus stocks are dangerous [Commentary]

The only known stocks of the deadly smallpox virus are now kept in two designated research laboratories, one in Russia and one in the United States. This has troubled many who believe that destruction of the virus would provide greater assurance that it would never again threaten the world.

Some scientists, however, insist that the intact smallpox virus is essential for their studies of new vaccines — even though the vaccines themselves are entirely different viruses.


The decision to destroy the virus has thus been debated and postponed repeatedly in the World Health Assembly over the past 15 years. It was decided, however, that this year's assembly should finally resolve the matter. A special expert committee of scientists was appointed to study the issues and to render advice. That committee agreed unanimously that the virus was not required and the stocks should be destroyed while another committee concluded the opposite, and in May, the assembly postponed action once again.

A little over a month later in July, six forgotten vials containing smallpox virus were found in an old National Institutes of Health laboratory. They had been prepared in 1954 for research use. In sealed vials, they posed no risk, but they served to recall the ever-present threat of smallpox and to reignite the debate once more.


In 1980 the world-wide eradication of smallpox was declared. All countries stopped vaccination, and no cases of smallpox have been detected for 35 years. To reduce the risk of virus escaping from a laboratory, the World Health Organization asked laboratories to destroy their virus samples or to transfer them to one of two research laboratories. Eventually, each country reported compliance. Nevertheless, the possibility that some specimens might be retained, either inadvertently or deliberately, was acknowledged.

Following eradication, a WHO international expert committee oversaw many studies of smallpox viruses from different regions. In 1995, these studies concluded. Five major professional associations of microbiologists recommended that the virus be destroyed. The 1996 World Health Assembly was asked to endorse the recommendation but decided to postpone action until a new smallpox vaccine could be developed. Since then, the question of virus destruction has been debated and postponed in five subsequent Health Assemblies, most recently this spring.

Do we need a new vaccine? No country is now using smallpox vaccine and none intend to resume vaccination. An outbreak of smallpox is highly unlikely but the probability is not zero. Escape of virus from a laboratory is one source; a second would be a terrorist using a hidden stock of virus. Thus, an adequate reserve supply of vaccine remains a high priority .

In 2002, the U.S. procured more than 200 million doses of a vaccine (called ACAM200) for a cost of $3.00 per dose. It is closely related to the vaccine routinely used throughout the U.S. for over five decades. Protection is provided within 5 days after a single dose. The vaccine is heat-stable and can be stored almost indefinitely. The vaccine was in routine use until 2002 despite the drawback that infrequently, it could cause adverse reactions in those with eczema or deficient immune responses. Some cardiac symptoms were also observed but without long-term complications. Compared to the frightening death rate of smallpox itself, possible complications were considered a small price.

Costs for the development and production of a new vaccine are great. Imvamune, a prospective, still unlicensed new vaccine has recently been acquired for the national stockpile. The cost for this vaccine for just 10 million people was more than $500 million. It may be safer for those with eczema or immune deficiency diseases, but, so far, it has been given to fewer than 8,000 people. It requires syringe and needle injection of two doses, 30 days apart. Adequate protection is not achieved until 45 days after the first dose. I cannot envisage how this vaccine might be used. No other candidate vaccines are on the horizon.

A smallpox outbreak anywhere in the world is a major global threat, what with travel and a highly susceptible world population. However, not more than 10 to 15 countries have sufficient vaccine to counter an epidemic. At this time, it would seem most prudent to be prepared in every way possible. Destroying the known existing stocks of the virus and augmenting the world's supply of a well-tested smallpox vaccine should have the highest priority.

Dr. D. A. Henderson is the former director of the WHO Global Smallpox Eradication Program and a Johns Hopkins University Distinguished Service Professor. His email is

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