Microsoft founder Bill Gates, his wife Melinda French Gates and British Prime Minister David Cameron at the World Economic Forum on January 28, 2011, in Davos, Switzerland.
Johannes Eisele/AFP/Getty Images
A study that measured antibodies and the disease history of more than 200 kids found that two doses of vaccine were 98 percent effective in preventing chickenpox compared with 86 percent for a single dose.
A man helps his dengue fever-stricken daughter in Tegucigalpa, Honduras. In June, Honduran authorities declared a state of emergency due to the high rate of dengue cases reported around the country.