Polio Experts Strive to Understand a Puzzling Outbreak

Health authorities in Namibia are scrambling to vaccinate the entire population, some 2 million people, against poliovirus, which has resurfaced after a 10-year absence in a highly unusual—and deadly—outbreak. Unlike most outbreaks, this one is targeting adults rather than young children. Outbreaks among adults are “as rare as hen's teeth,” says Bruce Aylward, who directs the global campaign to eradicate polio from World Health Organization (WHO) headquarters in Geneva, Switzerland, because adults usually have acquired immunity either through vaccination or exposure to infected children. But when an adult in infected, the disease tends to be much more severe.