After 26 years of waging a largely successful fight against polio, the World Health Organization declared an international public health emergency on May 5 when the virus turned up in nine countries. A year earlier, it had been confined to just three. The spread threatened the organization’s goal of eradication: Health workers reported 77 confirmed cases by early May, and with the high transmission season just getting into gear, the disease was on track to far outpace last year’s prevalence. WHO officials said the virus had jumped across the borders of Pakistan, Syria, and Cameroon into neighboring countries, and called on the three nations to vaccinate international travelers immediately.
Most of this year’s cases have occurred in Pakistan. There, guards with rifles accompany polio vaccine workers—many of them women—because of the risk posed by militants who have murdered dozens of workers since 2012. The most recent killing occurred in March, when armed men dragged a 30-year-old polio worker and mother of five from her home in the middle of the night and shot her to death. Pakistani suspicion of immunization campaigns was stoked after the CIA used an agent posing as a vaccine worker to discover the whereabouts of Osama bin Laden in 2011. Radical clerics have called polio vaccination a Western plot to sterilize Muslim men, and some parents still refuse to allow their children to take the oral drops.
Polio spreads most easily in regions with poor sanitation. Many people with the virus exhibit no symptoms, but it sometimes causes paralysis or death, and mainly affects children under 5. There is no known cure.
1894: First U.S. outbreak occurs in Vermont
1916: 6,000 die in an American epidemic
1952: The United States reports a record 57,638 cases
1953: Jonas Salk develops injectable polio vaccine
1961: Albert Sabin develops oral polio vaccine
1988: World Health Organization launches eradication initiative, estimating 350,000 cases worldwide
1994: North and South America declared polio-free
2002: Europe declared polio-free
2012: Virus remains endemic only to Afghanistan, Pakistan, and Nigeria