Stability of live, freeze-dried virus vaccines

Stability of live, freeze-dried vaccines is a major factor for successful vaccinations. Vaccines may be stored at -20 degrees C or less for long periods without loss of activity and this storage does not affect stability during subsequent storage. Storage in the refrigerator for long periods is harmless for certain very stable vaccines such as influenza, rubella, NDV, Marek's. Other vaccines, such as IBV, show a significant loss in titer after 2 years. The routine use of an accelerated stability test, e.g. exposure of each lot manufactured to 37 degrees C during 7 days, provides useful information regarding the stability of the vaccine at +4 degrees C. In general the loss during the accelerated stability test is higher than the loss after 24 months storage in the refrigerator. Specifications requiring that each vaccine lot must possess, after the accelerated test, a titer equal to or higher than the minimum titer needed for immunization, are a guarantee of sufficient potency at the time of administration. To solve the problems in tropical countries stable vaccines are essential. Cendevax and Rimevax exposed to tropical temperatures still possess the minimum required titer after several days.