The chicken pox shot for your older child might come as a two-for-one special for your baby. Varicella (chicken pox) immunization shots not only protect the child who is vaccinated, but also protects infants who come into contact with the child. Why no pox when older siblings get a shot? Since 1995, variella vaccines have been offered to children 12 months and older. But younger babies who aren't old enough to get the vaccine appear to be protected through so-called "herd immunity," the LA Times reports. Because fewer older kids develop chicken pox, the younger children are less likely to be exposed to the virus—and less likely to develop it.
Sticking with the herd really seems to have its benefits. Researchers studied data on chicken pox cases near Los Angeles and in Philadelphia during the first 14 years the vaccine was available. Herd immunity had a very powerful effect: as children over a year old began receiving the varicella vaccine, chicken pox in infants up to 11 months old fell nearly 90 percent between 1995 and 2008.
"This benefit reinforces the importance of maintaining high rates of varicella vaccination in the community to protect individuals who cannot be vaccinated because of age or medical contraindications," the researchers write.