One factor that may influence vaccine vial temperatures in vaccine refrigerators is adequate spacing of vials and vials in secondary containers. Vaccine potency can be reduced when vaccines are not properly stored or handled, resulting in poor protection against disease. There is also danger in the public losing trust in vaccines and providers if they require revaccination due to vaccines being compromised. World Health Organization (WHO) provides guidance in Immunization in Practice (Module 2: The vaccine cold chain) to leave vaccines in their original packaging when stored in refrigerators and to space the containers at least 2 cm apart to allow for air circulation. The Centers for Disease Control and Prevention (CDC) provide vaccine storage guidelines but do not give a specific distance to space the vials and their containers. Instead, they instruct the user to make sure the containers are not spaced too tightly.

The WHO Performance, Quality and Safety (PQS) working group for cold chain equipment was interested in confirming the need for spacing and verifying the current recommendations for spacing vials at least 2 cm apart. The testing described in this document investigated the thermal effects on vaccines of spacing secondary containers 2 cm apart. Additionally, this document explores other storing and packaging configurations and separation distances to identify the most appropriate storing strategies. Secondary packaging separation distances of 0 cm and 10 cm were tested in order to understand the effect of having no separation distance and having a large separation distance. All testing was completed in a Vestfrost ice lined chest refrigerator.