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Measles vaccine may be more effective if administered slightly later


A new research study published in Clinical Infectious Diseases has demonstrated that the MMR vaccine (measles, mumps and rubella) was more effective in teenagers who received their first dose of the two dose series at 15 months rather than at 12 months. The study was based on a more than 750 cases in 2011 of measles were reported in Quebec, Canada. Those individuals had received the routine 2-dose measles immunization schedule which is given at 12 and 18 months of age, which had been in effect in Quebec since 1996. This study assessed the effectiveness of this schedule during this outbreak that occurred during high school.

The authors determined that the risk of measles in 2-dose recipients was 3-4X higher when vaccine was first administered at 12 months of age compared with ≥15 months of age. They considered the data statistically significant. 

However, an recent editorial commentary has argued that it was a “rare event”, and this is just one geographic area. We could even argue that it’s just one batch or batches of vaccine involved, 15 years ago. In fact, with such a small group, it may be difficult to make a really solid conclusion.

According to The Canadian Press, Dr. Gaston De Serres of Quebec’s provincial public health agency, who was lead author of the article, does not think that the Canadian government will be adjust the dosage schedule on the basis of the study. Dr. De Serres stated that, “For Canada I would probably say that at this time we will not change the schedule. We need to follow up with more studies.”

I’m personally a bit skeptical that this study warrants a reconsideration of changes in vaccine scheduling, until more studies are provided. I think it qualifies as “intriguing” more than conclusive. But that’s how science based medicine works, you build up evidence until a compelling argument can be made to change medical practice.

Right now, the evidence still says the MMR vaccine prevents measles. Even in this study, fully vaccinated students were “attacked” (their words, not mine) by measles at a 4.8% rate. Non vaccinated students, 82%. That’s a huge difference by any statistical measure. And if you think measles is some innocuous disease, then think again:

Even in previously healthy children, measles can be a serious illness requiring hospitalization. As many as 1 out of every 20 children with measles gets pneumonia, and about 1 child in every 1,000 who get measles will develop encephalitis. (This is an inflammation of the brain that can lead to convulsions, and can leave the child deaf or mentally retarded.) For every 1,000 children who get measles, 1 or 2 will die from it. Measles also can make a pregnant woman have a miscarriage, give birth prematurely, or have a low-birth-weight baby.

I think this story bears watching. Maybe in the next few years there will be a change in the MMR vaccine schedule, to better protect children from measles.

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