What’s Behind the Latest Measles Outbreaks?
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Quebec’s Measles Outbreak
The largest measles outbreak in North America this year has been in the Canadian province of Quebec, where 757 cases were confirmed as of Oct. 5. A quarter of the cases were in people who had written proof that they’d received both doses of the MMR vaccine, while an additional 10% reported being immunized, says Gaston de Serres, MD, PhD, a medical epidemiologist at the Quebec Institute of Public Health and co-author of two studies about the Quebec outbreak that will be presented at the infectious diseases meeting.
De Serres will report on 100 cases that occurred in a single high school. At that school, half of the students who came down with the measles had been fully immunized against the disease.
He says he suspects that has to do with the fact that Canadian doctors recommend getting the first dose at 12 months, while U.S. doctors give parents a grace period of 12 to 15 months. The vaccine contains live measles virus, and at 12 months, babies may still have measles antibodies from their mothers that would attack the virus, lessening the vaccine’s effectiveness.
Plus, Canadian doctors recommend administering the second dose at 18 months, while U.S. doctors advise waiting until children are about to enter kindergarten, at about age 4 or 5.
However, de Serres says, he’d be uneasy saying the Canadian policy should change on the basis of his findings alone.
These studies will be presented at a medical conference. The findings should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.