Where could the next outbreak of measles be?

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Even as more American children are getting immunized against measles, diphtheria and other diseases, public-health officials are increasingly worried about potential outbreaks of these illnesses in certain pockets of the country where vaccination rates are dangerously low.
Parts of Oregon, Washington state, Idaho, Montana and a few other states have some of the lowest rates of compliance with vaccination guidelines—and the problem is growing, health officials say. Overall vaccination rates in some of these communities are under 80%, far below the threshold that is needed to prevent an outbreak for certain diseases. Exemptions in many states for philosophical or religious reasons allow parents to opt out of requirements for children to be vaccinated before entering school. Other parents delay immunizations for their young children, leaving them exposed to possible infections for a longer time.
Health experts say a community needs about 95% of its citizens to be immunized against measles to ensure herd immunity, where vaccinating a large percentage of a population keeps even unvaccinated people from getting the disease. Even people who aren’t vaccinated, such as newborns, get some protection from herd immunity as the disease remains limited to a small part of the community. Measles is a highly contagious respiratory condition that can lead to encephalitis, pneumonia and death. Other diseases, depending on how contagious they are, require other rates of immunization for a community to benefit. For mumps, 88% need to be immunized, and for chickenpox and polio the rate is 90%. “The Northwest is a black hole for religious exemptions” from vaccination, says Lorraine Duncan, immunization manager in the Oregon Health Authority’s Public Health Division. Last year, 5.6% of Oregon kindergartners had a religious exemption for vaccines, up from 2% a decade ago, Ms. Duncan says. In some school zones around Eugene and Portland, more than 10% of children have religious exemptions, and in pockets of the state’s southwestern corner, exemption rates are more than 20%, she says.

The Wall Street Journal

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