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Tuesday, November 29, 2011

Harpocrates Speaks: Varicella Vaccination Among Older Kids Protects Infants

Another timely article from Todd W.

Varicella Vaccination Among Older Kids Protects Infants

Turning on the news this morning, I was greeted with a story that caught my ear. Published online, ahead of print, a new study in the journal Pediatrics, "Varicella in Infants After Implementation of the US Varicella Vaccination Program", looked at the incidence of varicella (chickenpox) among infants under 12 months of age.

The varicella vaccine was approved in 1995 and is recommended for all children aged 12 months to 12 years. It is a "live" virus vaccine, meaning that the vaccine uses intact, though weakened, virus particles that grant immunity without causing full-blown disease. Vaccines of this sort are generally more effective than "killed" virus vaccines, which only use part of the virus. Because of the approved age range for the vaccine, it does not provide direct protection to infants under 12 months of age, but it can provide protection through herd immunity.

So what did the researchers find?

In the observational study, the authors looked at chickenpox incidence among infants under 12 months of age from 1995 to 2008. The population was broken up into 0-5 months and 6-11 months. They found that incidence among the total infant population fell 89.7% over the period examined. They also noted that complications and severity of disease was lower in the younger age group vs. the older group. The authors speculate that this may have been due to maternal antibodies (which generally provide some protection to infants for about 6 months).

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