TORONTO - A second study from Quebec is calling into question the timing at which children are vaccinated against measles.
The new research supports an earlier study from the same scientists which suggested the measles vaccine might work better if the first dose was given a few months later than the current practice.
Lead author Dr. Gaston De Serres of Quebec's provincial public health agency presented the work at a major international infectious diseases conference in San Francisco.
Quebec had a large outbreak of measles in 2011, with more than 700 cases reported.
Surprisingly, a number of the teenagers infected had received the recommended two doses of vaccine.
A study De Serres did last year showed those who got their first shot at 12 months of age were three times more likely to get infected than those who got their first shot at 15 months of age; his new study put the risk at six times more likely.
A measles expert from the U.S. Centers for Disease Control says public health has to strike an important balance in setting the timing for measles vaccine delivery.
Measles can be fatal for babies. So the goal is to give the vaccine as soon as it is effective to give children protection against the disease, Dr. Jane Seward says.
But measles vaccine doesn't work in young babies if it's given too early because antibodies they get from their mothers while they are in the womb counteract the vaccine.
The risk-benefit ratio of waiting a few more months to give the first dose of measles vaccine would likely be different in Canada, where measles cases are rare, than in a place like India, where the disease remains endemic.
Still, De Serres says Canada probably won't change its delivery schedule at this time, but needs to keep watching the situation.