Julio Valenzuela, 11, smiles as he gets a Measles, Mumps and Rubella vaccination (MMR), at a free immunization clinic for students. (ROBYN BECK/AFP/Getty Images) From January to April this year, there have been more measles cases in the United States than any year since 1996, according to data from the U.S. Centers for Disease Control and Prevention. Fifteen distinct outbreaks have occurred, accounting for 69 percent of the 187 CDC-confirmed measles cases. In total, the disease has been detected in...