A sneaky virus has infected 20 million Americans. For most, it's just an inconvenience, causing unattractive lesions. But for some, the infection leads to cancer, killing 250,000 people worldwide and costing billions in medical expenses every year. The vast majority of people who develop the cancer live in low-income countries, where it has become the most common type of cancer in women. After years of research, a company has released a vaccine that prevents nearly 100% of infections by the four forms of the virus that cause most of its problems. The question is: How much should such a life-saving vaccine cost?