A little over two decades ago, the World Health Organization (WHO) declared the official eradication of smallpox, the deadliest disease in recorded history, responsible for an estimated 300 to 500 million deaths in the past century.

This past summer, however, eight Russian children acquired a form of the virus after playing with ampoules of smallpox vaccine they found in a garbage dump outside of Vladivostok. Though the children did not contract full-blown smallpox, the incident reveals the threat still posed by the virus. As security in facilities holding vaccines and remaining live samples of the virus continues to deteriorate, the danger of smallpox has resurfaced.

For many centuries, smallpox was a widely accepted fact of life. In 1796, Dr. Edward jenner discovered the first effective smallpox vaccine. In 1967, using modern smallpox vaccines and increasing global health coordination, the WHO began its campaign to eradicate the disease. By 1980 the WHO declared smallpox to be officially eliminated.

The deadliness of smallpox is due in large part to its high fatality rate even with medical care 30 percent of those who contract smallpox die from it. But smallpox also possesses other properties that contribute to its lethality. Its incubation period is relatively long: full-blown symptoms develop only 12 to 14 days after infection, giving the virus ample time to spread unchecked and unnoticed. Highly durable in cold, dry weather, the virus can survive in open air for more than 24 hours in winter conditions.With its ease of delivery, rapid transmission, and long incubation period, smallpox is the ideal biological weapon, capable of being used by terrorists or rogue states alike and suitable for both complex ballistic missiles and simpler devices. A terrorist previously vaccinated against the virus could easily release it into a public area using a simple aerosol can.

Officially, the smallpox virus currently exists in only two places: the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia; and Vector, a former biological weapons factory located in Siberia. The virus's continued existence-and the threat of potential release-has caused contentious debate from the day of the announcement of its eradication. Since 1986, when the WHO Executive Committee on Orthopox voted to destroy all remnants of smallpox, the virus has enjoyed numerous stays of execution. On June 20, 1999, the last date set for eradication, the WHO decided to postpone action until 2002 "for the purpose of further international research into antiviral agents and improved vaccines, and to permit high-priority investigations of the genetic structure and pathogenesis of smallpox."

Opponents of the preservation of smallpox fear that as long as eradication is postponed, there is the possibility of unintended proliferation. Yet, as many observers note, the hidden motive for postponement may arise for much more disturbing reasons.According to estimates of the Henry L. Stimson Center, a public-policy institute focusing on security issues, more than 10,000 Russian biological and chemical warfare experts-many of whom have access to the smallpox virus-present a risk of deliberate proliferation. Some Russian scientists earn a mere US$100 per month. If offered the proper financial incentives, these scientists could easily supply the virus to an interested party.

Similar clandestine deals may already have occurred. US intelligence reports released in 1999 and 2000 purportedly cite several countries, including North Korea and Iraq, as possessing strains of the virus and possibly the means to use it.A KGB report released publicly in 1993 made first mention of the likelihood that North Korea had acquired the virus. Independent reports from US intelligence offices have found that samples of blood from North Korean soldiers showed signs of recent vaccination for the virus, implying that North Korea was preparing its troops for a possible offensive deployment of the virus. Coupled with North Korea's August 1998 ballistic missile test over Japan, this news signals that the North Korean government possesses all the necessary elements to deploy the virus. Evidence also suggests that Iraq recently manufactured the smallpox vaccine, again implying that the government has the virus in its arsenal. Other groups suspected of holding smallpox range from Osama bin Laden's terrorist organization to Japan's Aum Shinrikyo sect, which was responsible for releasing sarin nerve gas in a Tokyo subway in 1995.

Such ominous indications of the virus's proliferation support the argument that protective measures must be implemented. A few scientists and politicians have gone even further and advocated the outright eradication of all remaining stores of the smallpox virus. D.A. Henderson, the leader of the WHO eradication campaign, and other proponents of the virus's destruction argue that by eliminating official stores, the WHO can make possession of smallpox a crime against humanity. In doing so,WHO officials hope to persuade terrorists and certain states to destroy their stocks. Opponents of these measures see eradication of the virus as suicidal: the best guard against unknown stores of smallpox is smallpox itself. With the virus on hand, research on treatment methods and vaccines can continue until world-health officials can declare with certainty that the virus exists nowhere else on earth.

Ironically, the WHO's successful immunization campaign may have made the world even more vulnerable to smallpox. In most cases, immunity gained from the vaccine is severely weakened after ten years. Since worldwide vaccination for smallpox ended over 20 years ago, the vast majority of the world's population is once again vulnerable to the disease. The reemergence of smallpox, especially given the virus's suspected proliferation, is thus a plausible danger.

In the event of an outbreak, authorities have traditionally attempted to check the virus by isolating patients and people in close contact with them and vaccinating the population in the outbreak area. The intent is to seal off the virus by encircling it with a wall of immunity, preventing it from spreading further. This method requires both a substantial supply of the smallpox vaccine and a pre-established hierarchical command structure to implement the quarantines and vaccinations.

Currently, most countries are in a poor position to respond to an outbreak. The Johns Hopkins Center for Civilian Biodefense Studies estimates that only 50 million to 100 million doses of the vaccine exist in the world today. Furthermore, epidemiologists are concerned about the quality of these vaccines, many of which were manufactured using older methods.