The warm chain : a critical problem for national immunization programs in temperate and colder climates

The management of vaccines in immunization programs has largely focused on preventing heat damage and on detecting vaccine freezing. The winter freezing of vaccines has been identified as a serious operational problem in the diphtheria epidemic in the Newly Independent States (NIS) of the former Soviet Union. Other regions of the world face similar vaccine storage conditions and risks. This paper, presented at TECHNET, a global consultation on logistics for health, estimates the scale of the problem of toxoid vaccine freezing in immunization programs. Toxoid vaccine stability data are reviewed and summarized, and regions of the world with average night time temperatures below four degrees Celsius are identified. The problem is described in detail using temperature measurements, field observations, and epidemiological data from countries in the NIS. Recommendations to support the development of appropriate vaccine storage refrigerators are presented, along with recommendations for safe vaccine transport in colder climates. (Author abstract, modified)