...CDC also advises use of two-doses of chickenpox vaccine to boost protection

The US Centers for Disease Control and Prevention (CDC) reports that its Advisory Committee on Immunization Prevention has voted to recommend the administration of a second dose of varicella (chickenpox) vaccine to children aged four to six, in an effort to further improve protection against the disease.

The advice is based on the results of a controlled study in 2,216 children between the ages of 12 months and 12 years that compared one dose varicella vaccine (Merck & Co's Varivax) to two doses over a 10 year observation period. Analysis of the data showed that a single administration of the vaccine was 94.4% effective, whereas a repeat administration conferred protection in 98.3% of those treated. Over a 10-year period, this translates into a 3.3-fold lower risk of developing chickenpox more than 42 days after vaccination.

Single vaccination not uniformly effective