Bill Gates walked into the World Health Organization's headquarters in Geneva -- for a meeting in an underground chamber where global pandemics are managed -- and was greeted by bad news. Polio was spreading across Africa, even after he gave $700 million to try to wipe out the disease.

That outbreak raged last summer, and last weeka new outbreak hit Tajikistan, which hadn't seen polio for 19 years. The spread threatens one of the most ambitious health campaigns in the world, the effort to destroy the crippling disease once and for all. It also marks a setback for the Microsoft Corp. co-founder's new career as full-time philanthropist.