The “endgame” in the decadeslong campaign to eradicate polio suffered major setbacks in 2019. From a report: While the effort lost ground in Afghanistan and Pakistan, which recorded 116 cases of wild polio — four times the number in 2018 — an especially alarming situation developed in Africa. In 12 countries, 196 children were paralyzed not by the wild virus, but by a strain derived from a live vaccine that has regained its virulence and ability to spread. Fighting these flare-ups will mean difficult decisions in the coming year. The culprit in Africa is vaccine-derived polio virus type 2, and the fear is that it will jump continents and reseed outbreaks across the globe. A brand new vaccine is now being rushed through development to quash type 2 outbreaks. Mass production has already begun, even though the vaccine is still in clinical trials; it could be rolled out for emergency use as early as mid-2020. At the same time, the Global Polio Eradication Initiative (GPEI) is debating whether to combat the resurgent virus by re-enlisting a triple-whammy vaccine pulled from global use in 2016. That would be a controversial move, setting back the initiative several years, as well as a potential public relations disaster — an admission that the carefully crafted endgame strategy has failed. “All options are on the table,” says viro-logist Mark Pallansch of the U.S. Centers for Disease Control and Prevention, one of the five partner organizations in GPEI. “We are clearly in the most serious situation we have been in with the program,” adds Roland Sutter, who recently stepped down as the director of polio research at the World Health Organization (WHO). The heart of the problem is the live oral polio vaccine (OPV), the workhorse of the eradication program — the only polio vaccine powerful enough to stop viral circulation. Given as two drops into a child’s mouth, OPV for decades contained a mix of three weakened polio viruses, one for each of the three wild serotypes that have long plagued humanity. All three serotypes in the vaccine have the potential to revert to more dangerous versions; that’s why the endgame strategy calls for deploying OPV in massive campaigns to eradicate the wild virus, then ending its use entirely.