“Just because you need a third dose doesn’t mean the two dose schedule is having issues or anything”

February 16, 2010 by · 2 Comments
Filed under: CDC Watch, News, Opinion, Parents' Pages, Vaccine/Disease Analysis 

Mumps story:

Because of continued spread, health authorities working with communities in Orange County are giving schoolchildren a third dose of the MMR vaccine. Gallagher says it will be two or three months before it’s known whether the effort succeeded.

Why do they need a third dose?

The infections happened despite high coverage with the measles-mumps-rubella (MMR) vaccine. Among patients ages 7 to 18 — the age group that had the most cases — 85% of patients had received the two recommended MMR vaccine doses.

This doesn’t mean the MMR vaccine isn’t working, says epidemiologist Kathleen Gallagher, DSc, MPH, the CDC’s team leader for measles, mumps, and rubella.

“Two doses of mumps vaccine is believed to be 90% to 95% effective,” Gallagher tells WebMD. “But that means people can still get mumps. If the vaccine is 90% effective and 100 people are exposed to mumps, 10 will get the disease.”

If we imagine that mumps is being sprinkled from the sky and spread evenly throughout the population, then yes, one out of ten vaccinated people would catch mumps if the vaccine was, indeed, 90% effective, or one out of twenty if it were 95% effective. But if the vaccine creates “herd immunity” then the disease shouldn’t be able to jump from vaccinated person to vaccinated person to vaccinated person. Read more

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