Evaluation of an outside-the-cold-chain vaccine delivery strategy in remote regions of western China
Vaccines are temperature-sensitive biological products. Exposure to heat shortens a vaccine's shelf life,1 while freezing vaccines that should not be frozen causes irreversible loss of potency.2 Therefore, maintaining vaccines inside the cold chain (ICC) is an essential part of a successful immunization program. However, in many developing countries in Asia, a cold-chain infrastructure is not available, especially in remote and rural areas.3,4 Some people live in remote areas of the western plateau of China, far away from the county health center, and there is no cold-chain infrastructure. As a strategy to extend vaccination coverage, some local health units have suggested winter delivery of vaccines, relying on ambient temperatures outside the cold chain (OCC). Areas in China's western plateau at 3,000 to 5,000 meters above sea level have an extreme continental climate with long, cold winters. The mean temperature during November, December, and January (the coldest period) ranges from −22°C to −3°C, and the ambient temperature is sub-zero from the beginning of October to the end of April. For some health unit workers, the term “cold chain” implies, incorrectly, that avoiding heat is the sole objective, and that unduly low temperatures would not be an issue for vaccine storage and delivery. We conducted the fieldwork for this survey in November 2007. Our objective was to investigate whether hepatitis B (HepB) and measles vaccines stored and transported in the winter were subjected to below freezing and/or high temperatures during the routine distribution of vaccines to peripheral health centers in remote regions of China's western plateau. We designed the study to assess the effects of exposure to temperatures OCC on vaccine potency.