More and more parents are refusing to get their children vaccinated because they think that the shots aren't adequately tested or could cause autism. But when parents refuse vaccines over concerns about their own children, they may put the health of all children at risk. Putting it another way, having your kids immunized against infectious disease can be considered an altruistic act.
That's the message in a new study on how "herd immunity" combats infectious disease. It's a notion that's been around for centuries: When enough people in a population are vaccinated, disease can't spread, even if some people (such as those who, because of suppressed immune systems or other health problems, can't get the shots) aren't. About 75 to 95 percent of a group needs to be vaccinated for herd immunity to work; the proportion varies depending on how efficiently a given bug spreads. An 85 percent immunization rate halts polio, while more than 90 percent of a group needs to be vaccinated to derail pertussis. Rates of pertussis, measles, and mumps have been increasing in the past few years as more and more parents refuse vaccines.
We have the Hutterites, an Anabaptist religious group similar to the Amish, to thank for a fresh example of how an entire community can benefit when individuals are willing to be immunized. Researchers asked residents of 49 Canadian communities of Hutterites, each with 60 to 120 people, to take part in a study of seasonal flu vaccine. About 1,000 children ages 3 to 15 were vaccinated. Children in 25 colonies got flu vaccine, while children in 24 other colonies were immunized against hepatitis A as a control. According to results published online by the Journal of the American Medical Association, just 4.5 percent of all people living in the flu-shot colonies got flu that year, compared with 10.6 percent in the control group. That translates to 61 percent indirect protection for unvaccinated people. No one in either group suffered serious side effects.
This new study gives a much clearer view of the power of herd immunity than previous studies because the Hutterite colonies are relatively isolated. The new federal recommendations that all Americans over 6 months old get seasonal flu shots is based partly on the notion that preventing the spread of flu among children will reduce the risk to the elderly, whose immune systems respond poorly to vaccines and who face the greatest risk of death from influenza.
So when you're thinking about the pluses and minuses of childhood vaccinations, consider also the Hutterites and the benefits conferred when communities join together to protect all who live there.
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