Measles cases have surged in parts of Canada and the United States this year. A still smoldering outbreak of measles in Quebec is the largest in the Americas in over a decade. An investigation into an outbreak in a high school in a town that was heavily hit by the virus found that about half of the cases were in teens who had received the recommended two doses of vaccine in childhood - in other words, teens whom authorities would have expected to have been protected from the measles virus. It's generally assumed that the measles vaccine ... should protect against measles infection about 99 per cent of the time. So the discovery that 52 of the 98 teens who caught measles were fully vaccinated came as a shock to the researchers who conducted the investigation.