In May 1980, the World Health Organization officially declared that smallpox had been eradicated from human existence — a disease that had killed approximately 300 million people in the twentieth century alone and traced back at least 3,000 years to the smallpox pustules found on the head of the mummy of Pharaoh Ramses V

The last person to catch smallpox naturally was a 23-year-old Somali hospital cook named Ali Maow Maalin, who was diagnosed on 26 October 1977 in the town of Merca on Somalia’s Indian Ocean coast. He survived. Approximately 300 million other people, across the preceding 80 years of the 20th century, had not. Smallpox had, for at least 3,000 years of documented human history, been one of the more substantial single causes of premature human mortality on the planet — killing, on the accumulated 20th-century evidence, approximately three times as many people as all the wars of the same century combined, disfiguring approximately 65 to 80 percent of the survivors with the deep pockmark scars the variola pustules characteristically produced, blinding approximately 5 to 9 percent of them through the ocular complications of the acute phase of the disease, and contributing substantially to the demographic collapse of essentially every civilisation the disease reached that did not have prior immunity to it (the Aztec Empire lost approximately 3 million people to a single 1520 outbreak; the pre-Columbian Native American populations lost approximately 90 percent of their pre-contact demographic totals to smallpox and the other Old World diseases that accompanied it; the 18th-century European population lost approximately 60 million people to it across the single century). The earliest verified evidence of smallpox in the human archaeological record is the mummified remains of the Egyptian Pharaoh Ramses V, who died in 1157 BCE and whose mummified head — which the Australian-born anatomist Grafton Elliot Smith, working as Professor of Anatomy in Cairo, examined in the early 1900s and published in his 1912 catalogue The Royal Mummies — shows the specific pustule pattern that variola infection produces on the human face and scalp.

According to the World Health Organization’s official 2020 commemoration of the 40th anniversary of the smallpox eradication, the specific mechanism by which the 20th-century international public-health community managed to accomplish what the preceding 3,000 years of human medical science had failed to accomplish was a coordinated 13-year vaccination programme executed between 1967 and 1980 at a total cost of approximately $300 million, involving approximately half a billion individual vaccinations administered by thousands of health workers across essentially every country on the planet where the disease was endemic. The programme’s institutional architecture was designed by the American epidemiologist Donald A. Henderson, who directed the WHO Smallpox Eradication Programme from 1966 to 1977 from an office in Geneva that Henderson later described as “the size of a broom closet.” Its critical strategic innovation was developed by Henderson’s colleague William Foege, a Centers for Disease Control epidemiologist working in Nigeria in 1966: rather than attempting to vaccinate the entire population of every endemic country (which was economically and logistically impossible given the vaccine supply available), Foege proposed identifying each individual smallpox case as it occurred, systematically tracing every person who had had contact with that case, and vaccinating the specific “ring” of contacts around each case to prevent the disease from spreading beyond them. The strategy — subsequently known as “ring vaccination” — worked substantially better than any mass-vaccination approach that had been attempted anywhere previously.

How the disease actually ended

The final ten years of smallpox eradication followed a specific geographic sequence that has, in the subsequent 45 years, been the subject of substantial detailed epidemiological reconstruction. As detailed in the US Centers for Disease Control’s official history of the global smallpox eradication programme, smallpox was eliminated from Brazil (and the rest of South America) in 1971, from Indonesia in 1972, from India (which had been one of the disease’s most substantial reservoirs, with an estimated 60,000 cases per year at the programme’s start) in 1975, from Bangladesh in 1975, and from Ethiopia in 1976. The last three endemic countries — Ethiopia, Kenya, and Somalia — required a substantial additional effort because of ongoing civil conflicts in the Horn of Africa that limited the WHO field teams’ access to the affected populations. The 1977 Somali case involving Ali Maow Maalin represented the last case anywhere in the world of naturally-transmitted variola. The last case globally — a British medical photographer named Janet Parker, who worked at Birmingham Medical School and died at East Birmingham Hospital in September 1978 after being infected by a laboratory sample of the virus stored at the University of Birmingham — prompted the substantial subsequent international debate about whether the remaining laboratory stocks of variola should be destroyed to prevent any possibility of accidental or deliberate re-release.

The final certification of eradication was issued by the Global Commission on 9 December 1979, following a two-year systematic review that involved sending WHO investigators to every country where smallpox had previously been endemic, examining hospital records for any suspected cases, testing serum samples from randomly-selected populations for evidence of ongoing variola circulation, and offering a $1,000 reward (subsequently raised to $10,000) to anyone who could produce a verifiable current case. No verifiable case was produced. The formal announcement in May 1980 was, in essential respects, a ceremonial ratification of a scientific determination that had already been made five months earlier.

The stocks that remain

The variola virus itself is not, however, completely gone. Per Our World in Data’s comprehensive review of the historical epidemiology of smallpox and its eventual eradication, two national laboratories retained frozen stocks of the virus after the 1980 declaration: the US Centers for Disease Control in Atlanta and the VECTOR State Research Centre in Koltsovo, Russia. The retention was originally intended as a temporary measure to allow scientists to complete the sequencing of the virus’s genome and to preserve reference samples for potential vaccine development in the event of an accidental re-emergence. The World Health Assembly repeatedly scheduled the destruction of these stocks — most notably in 1996, when resolution WHA 49.10 set a deadline of 30 June 1999 for their destruction — and the destruction has, on each of those occasions, been postponed. The current substantive rationale for continued preservation is that the possibility of deliberate re-release of the virus by a hostile state actor or a non-state biological weapons programme (a possibility that became substantially more concerning to Western governments after the anthrax mailings that followed the September 2001 terrorist attacks in the United States) requires the continued availability of the virus for defensive vaccine research. The counterargument — that as long as the virus exists in any laboratory anywhere, the possibility of accidental or deliberate release cannot be fully eliminated — has not, so far, produced a policy change. As reported in National Geographic’s summary of the current state of smallpox preservation and the ongoing debate over the remaining virus stocks, the disease that killed approximately half a billion humans across the recorded history of the species, that was formally eliminated from the global population in 1977, and that was formally declared eradicated in May 1980, currently exists in exactly two secure freezer facilities on Earth — and the question of whether those freezers should be emptied has, in the 46 years since the declaration, remained substantively unresolved.