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. The current study was designed to ascertain if HBV is subject to freezing temperatures during transport to rural health centers.
Methods: During several time periods from 2001 to 2003, HBV vaccine transported from the national vaccine store to provincial stores and from two provincial stores to rural health centers was monitored for freezing using 3M Freeze Watch indicators.
Results: Of 181 provincial-to-rural transports, 19% (95% CI 13-25%) resulted in freezing. One of 59 or 1.6% (95% CI 0-5.6%) of national-to-provincial store transports indicated freezing. In the second half of each substudy, freezing events diminished. Duration of transport was associated with freezing.
Conclusion: Identification of freezing temperatures during provincial-to-rural vaccine transport provides evidence that HBV vaccine is being damaged. This is the likely cause of the poor vaccine response in the Mongolian countryside. The authors speculate that packing vaccines for transport with ice taken directly from storage deep freezes at -20 degrees C is the cause of the freezing.