Validation of cold chain procedures suitable for distribution of vaccines by public health programs in the USA.

To enhance quality assurance of vaccine distribution by public health programs in the US, various methods for packing vaccines were validated. Validation involved both tests in an environmental chamber and actual shipping of packages by commercial overnight delivery service. Dry ice was used with vaccines needing to be kept at temperatures lower than -14 degrees C, and water-based cold packs with other vaccines. The latter could be used in two ways. When frozen, and placed over two or three faces of well-insulated boxes, assortments of vaccines were kept cold but not frozen for 2 days or more. However, packages with -15 degrees C cold packs may reach < 0 degree C. When cold packs at refrigerator temperature cover four to six faces of well insulated boxes, vaccine freezing in winter conditions or warming in temperate conditions was slowed considerably. These approaches, which require materials costing less than approximately 1% of the cost of the vaccines they protect, provide examples of packaging suitable for overnight delivery of vaccines in the US in different seasons.