Characterization of the freeze sensitivity of a hepatitis B vaccine.

Recent studies have revealed that vaccines containing aluminum adjuvant are exposed to sub-zero temperatures while in the cold chain more frequently than was previously believed. This raises concerns that these freeze-sensitive vaccines may be damaged and offer inadequate protection. This study was undertaken to characterize the immediate qualitative changes of one such vaccine, hepatitis B, caused by freeze exposure. Hepatitis B vaccine was subjected to freezing temperatures ranging from 0 degrees C to -20 degrees C for up to three episodes with durations ranging from 1 hour to 7 days. The vaccine was analyzed for freezing point, particle size distribution, tertiary structure, and in vitro and in vivo potency. Whether or not hepatitis B vaccine freezes was shown to be dependent on an array of factors including temperature, rate of temperature change, duration of exposure, supercooling effects and vibration. Vaccine exposed to "mild" freezing (-4 degrees C or warmer) temperatures did not freeze and remained qualitatively unaltered. Single or repeated freezing events at temperatures of -10 degrees C or lower were associated with aggregation of the adjuvant-antigen particles, structural damage of the antigen, and reduction of immunogenicity in mice. Damage to the vaccine increased with duration of freezing, lower temperature, and the number of freezing episodes. With vibration, vaccine froze at -6 degrees C after 1 hour and damage occurred. Freezing and freeze damage to vaccines containing aluminum salt adjuvant represent real risks to the effectiveness of immunization and should be prevented by strengthening the cold chain system or, alternatively, development of freeze-stable vaccine formulations.