Donald G. McNeil Jr., a science reporter for The New York Times, joins us with a look at what could be a significant breakthrough in the fight against the spread of HIV. Researchers have announced the results of a six-year, 16,000-person study in Thailand, and it appears that an experimental HIV vaccine has cut the risk of infection by almost one-third when compared to a placebo. This is the first time a vaccine has cut the risk of infection at all.