IDWeek 2020: Smallpox eradication offers lessons 40 years on, but they're not easy

Four decades after it was made official, the eradication of smallpox remains a unique achievement.

It is an achievement that stands as proof that a disease meeting the right biological criteria can, with the right strategy, be wiped from the face of the earth. But while attempted, it has not been duplicated. Nor, on examination, have the lessons the 13-year campaign to eradicate smallpox offered been applied on the scale to less ambitious goals -- the control of a pandemic, for example.

Those lessons from the successful campaign were the subject of the closing plenary of IDWeek, in a session that brought together a former Centers for Disease Control and Prevention "disease detective" who began his career working on the smallpox campaign, a member of the World Health Organizations's Strategic Advisory Group of Experts on immunization for polio as well as measles and rubella working groups, and a co-developer and director of the online Target Zero Smallpox Eradication Program Archive.

The latter, Dr. Leigh Henderson, who also is an epidemiologist and the daughter of smallpox eradication program leader Dr. D.A. Henderson titled her talk "What we can learn."

"I'm not calling it 'lessons learned,'" she noted, "because if we had learned, I wouldn't be here now."

Smallpox -- the disease itself, and the existence of a highly effective vaccine to control it -- met essential biological criteria to be a candidate for eradication, all three speakers noted: With no animal reservoir it was transmitted by humans, person to person only, it was only transmitted by symptomatic people, active illness was easy to identify with limited training, and administering the highly effective one-dose vaccine, effective even during the incubation phase of infection, also required minimal training.

That didn't make smallpox an easy target for eradication in 1967. With standards for vaccination not systematically monitored then, only 10% of those available were usable. As the campaign began in the pre-digital area, some of the most affected countries were only beginning to emerge from the plunder and fetters of colonialism. Poverty, civil unrest, warfare and natural disasters all spurred instability, migration and more opportunities for disease to spread than opportunities to control it. Well before the so-called "golden age" of international infectious disease responses, funding was tight; the entire 13 years, Dr. Henderson said, was funded at a total of $98 million, the equivalent of $519 million today. "Funds always fell short," she said. She finds the idea that the success of the program came easily "ludicrous."

"It was on the brink of failure constantly," she said. She heard about the disasters that threatened to derail the program regularly, over dinner.

What the program had going for it was political will, and strong cooperation, even among warring nations, that would suspend hostilities to enable vaccination efforts, former CDC Epidemic Intelligence Service Officer Dr. Jeffrey Koplan, who began his career with smallpox and now is vice president for global health at Emory University, said. Facilitating that cooperation was a central coordinating agency -- the World Health Organization. It also had a strong, informed, rigorous but flexible strategy. Mass vaccination -- vaccinating everyone health workers could reach was found not to be effective. Vigilant control through surveillance, including through markets and schools, tracing contacts of infected people and contacts of contacts -- a ring vaccination strategy --  was effective.

Repeating the success, with polio, with measles, does not mean repeating the strategy, however, WHO SAGE working group member Dr. Walter A. Orenstein, who also is associate director of the Emory Vaccine Center and the director of Emory Vaccine Policy and Development. It means focusing on and responding to the epidemiology of the disease, being prepared to change strategies, develop and sustain ongoing research, and demonstrating proof of principle with success in different communities, he said. Communication, to gain community buy-in and support are essential, he said, as are sources of funding and support.