Wikimedia, Centers for Disease Control and PreventionGiving
previously vaccinated children an additional dose of the
measles, mumps, and rubella (MMR) vaccine helped to control an
intense outbreak in a small, tight-knit religious community,
according to researchers from the Centers for Disease Control
and Prevention. The new study, published this week (November 5)
in Pediatrics, suggests that the intervention provided a herd-
immunity effect—where a significant part of a population with
immunity to a particular pathogen acts as a firewall to protect
the entire community by disrupting the chain of infection. The
researchers studied a mumps outbreak in an orthodox Jewish
community in Orange County, New York, in late 2009 in which 400
children from three schools fell ill. Most of the children in
the community had been vaccinated with the recommended 2 doses
but a combination of large families and crowded schools
overwhelmed that protection, the researchers say. So a third
vaccine was administered to children with