Exposure of hepatitis B vaccine to freezing temperatures during transport to rural health centers in Mongolia.

Background: A previous evaluation of the Mongolian hepatitis B virus (HBV) infant vaccination program showed that only 70% of rural subjects developed protective antibody levels compared to 94% of urban subjects. The difference is likely due to damaged vaccine being administered to rural infants. HBV vaccine is heat-stable, but freezing destroys immunogenicity.