Originally published in October 2011
An unusual vaccine observation from a large measles outbreak in Quebec may raise some alarm among those who attend the annual meeting of the Infectious Diseases Society of America.
Measles cases have surged in parts of Canada and the United States this year, with cases among unvaccinated children and teens driving the high numbers, public health officials from both countries will tell a major infectious diseases conference this weekend.
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, when given in a two-dose schedule in early childhood, 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.