On Jan. 31, Microsoft Corp. Chairman Bill Gates will appear during a live webcast to talk about worldwide efforts to eradicate polio. “ABC World News” anchor Diane Sawyer will moderate the event, which will be broadcast beginning at 8:30 a.m. at www.gatesfoundation.org. The webcast will include discussions with David Oshinsky, who in 2006 won a Pulitzer Prize for his book “Polio: An American Story,” as well as Helen Rees of the World Health Organization, and Ciro de Quadros, executive vice president of the Sabin Vaccine Institute. Since 1998, nearly 2.5 billion children worldwide have been vaccinated against polio. About 75 percent of global polio cases originate in northern Nigeria and northern India, as well as parts of Afghanistan and Pakistan.