Monday, March 15, 2010

New Proof for Herd Immunity

“Herd immunity” is one of the most important concepts behind vaccination – the idea that once a certain percentage of the population is vaccinated against a particular illness, the entire population will be protected even if not everyone has been vaccinated. While the concept has often been demonstrated, it has been hard to prove, but an innovative study published in the Journal of the American Medical Association provides such proof.

In a study funded by the American and Canadian governments, scientists from several Canadian universities and St. Jude’s Children’s Research Hospital in Tennessee conducted their research in 49 remote Hutterite farming colonies in western Canada. The Hutterites have similar roots to the Amish and live in small, isolated communities, making them perfect subjects for this research.

In 25 of the colonies, all children ages 3 to 15 received seasonal flu shots. In 24 other colonies, the same age children received the hepatitis A vaccine instead. In the colonies without the flu vaccine, more than 10 percent of the population had seasonal flu during that year’s flu season; less than 5 percent of the population in the vaccinated colonies did. This translates to a 60 percent “protective effect” for the whole community and suggests that giving flu shots only to children would still protect the elderly, even if they were not directly vaccinated.

While CDC recommends directly vaccinating high-risk individuals, such as the elderly, and has moved to recommending universal vaccination for the recent H1N1 epidemic, this study provides important evidence for the existence of herd immunity and supports the practice of vaccinating children to prevent further spread of influenza in the population.

Rebecca Barson
Consultant, Partnership for Prevention


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