Immunization rates against the human papillomavirus (HPV), the virus that causes cervical cancer, are amongst the lowest of all vaccine programs in the US, with fewer than one in four female teens getting the shot in many poor-income states, and often far fewer women than that get immunized in countries of the developing world. A major deterrent, public health experts warn, is the vaccine’s price—the two approved HPV vaccines are among the most expensive adult vaccines, often costing close to $400 in the US private sector for a full three-dose course of therapy.