Objectives: To study the impact of the use of cool water packs (water packs refrigerated at 2 to 8 degrees C) on the cold life of vaccine transport boxes and the shelf life of the vaccines.
Methods: Data loggers were used to measure the temperatures of vaccine shipments with cool water packs in laboratory studies and country evaluations. The temperature recordings were mathematically translated into reduction of vaccines shelf life, which are illustrated through degrees of color changes of Vaccine Vial Monitors.
Findings: Laboratory studies at extreme ambient temperatures (43 degrees C) showed that, with the use of cool water packs, temperatures inside the cold box rise to around 20 degrees C within 48 h. When this exposure scenario was repeated four times, the impact of the temperature history on the different heat stability categories of vaccines varied between 2.4 and 36.0% shelf life loss. Oral polio vaccine was found to be the most affected vaccine. All other vaccines were affected with 2.4 to 10.4% life loss. Country assessments (real life situation with temperature variations between day and night) showed between 0.4% to 4.6% life loss when the boxes were exposed to ambient temperatures ranging from 11.7 to 39.8 degrees C over the 98 h 15 min test period.
Conclusions: The use of cool water packs is found to be a legitimate and safe practice for vaccines other than oral polio vaccine, so that cool water packs can safely replace frozen icepacks without any serious consequences on the ability of vaccines to confer protection against disease.