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35 Who Made a Difference: D. A. Henderson

Eradicating one of history's deadliest diseases was just the beginning

Donald Ainslie Henderson, known to his friends as D.A., could never be accused of being wishy-washy. As President Bush's lead expert on bioterrorism—a post to which he was appointed one month after the September 11 terrorist attacks—he used language that government officials rarely do. When the FBI investigated a biologist for transporting infectious organisms in the course of research, he said the bureau had "lost all perspective." He has also spoken out against official policy by urging the destruction of all laboratory stockpiles of the smallpox virus and calling for a reassessment of the international strategy to wipe out polio.

Henderson's iconoclasm arguably led to his greatest accomplishment. Under his guidance, the World Health Organization (WHO) oversaw history's first—and, to date, only—vanquishing of an infectious disease, smallpox.

In its heyday, smallpox was a disease that spread with ease and deadly efficiency, killing a third of its victims. Its human toll dates at least to the time of the Pharaohs; in the 20th century alone, it killed 300 million people and left several million permanently disfigured or blind.

But for all its menace, the smallpox virus had qualities that, as Henderson, 77, recalls, "made this a relatively easy disease to eradicate." The vaccine was effective, long-lasting, relatively cheap, easy to administer, easy to transport, worked with only one dose and required no refrigeration. And smallpox infected only people, meaning that it could not hide out in "animal reservoirs" as so many infectious diseases do, biding its time until encountering an unprotected population.

During Henderson's tenure as WHO's chief medical officer for its global eradication program, smallpox cases were generally limited to Brazil, South Asia and most parts of Africa. WHO workers identified outbreaks readily, because every victim had a visible rash and almost every survivor was left with pockmarks. "If we went into a brand-new area, we could quickly tell whether they had any smallpox there or not," says Henderson. "We could look on the faces of people and know." Most people who were asked "When did you get those scars?" knew the year precisely. A brush with smallpox, he says, "was a very memorable event."

In the late 1960s and early '70s, conventional wisdom held that the way to eradicate a disease was to vaccinate entire populations. But Henderson thought that for smallpox, such a strategy would be expensive, tedious—and unnecessary. Instead, he used an approach known as ring vaccination. When a case was identified, the sick person was isolated quickly, and vaccine was given to all of the patient's primary contacts (relatives, neighbors, co-workers) and secondary contacts (the contacts of the contacts). In this way, outbreaks could be throttled with a vaccination rate of 50 to 80 percent.

The strategy worked. In October 1977, a young man in Somalia named Ali Maow Maalin became the last human case of naturally occurring smallpox in the world. (He survived.) In 1980, WHO declared the disease eradicated.

But eradication had a dark side. Now that there's no need to vaccinate anyone, the entire global population is vulnerable to smallpox. This makes the smallpox virus, known as variola, an ideal weapon for terrorists—or any evildoer who could, as Henderson once observed, make up a batch of virus pretty easily in "a good two-car garage."

To prevent this possibility, the WHO has consistently recommended killing off all remaining samples of variola. Only two such stockpiles currently exist, at least officially: one at a high-containment laboratory at the Centers for Disease Control and Prevention in Atlanta, the other in a Russian laboratory in Siberia. But the Clinton administration decided in 1999 not to destroy the CDC variola, a decision that has been reaffirmed by the Bush administration.

Henderson believes that the virus exists outside the two official labs, but he has argued that destroying the Russian and American specimens would send a message to all nations that harboring variola constitutes a crime against humanity.


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