A vaccine carrier's time is not one number; the catalogue figure is the result of a defined test. The empty carrier is held at 43 °C, frozen ice packs go in, the lid is closed and the time is measured until the warmest point of the vaccine compartment first reaches 10 °C. Under UNICEF's guideline carriers hold at least 15 hours (short range) or 30 hours (long range) in this test. Because the limit is 10 °C, the time inside the 2-8 °C range that vaccines need is shorter.
In the field four things shorten the time: high ambient heat in the sun or a heated vehicle, a half-empty carrier, the lid opened at every stop, and coolant that is not fully prepared. UNICEF states that the frequency and duration of openings shorten the life.
Preparation carries risk in both directions. In a standard carrier, packs used frozen straight from the freezer can freeze freeze-sensitive vaccines; WHO asks for the pack to be left until the ice moves freely when shaken (conditioning). In freeze-preventive carriers the reverse holds: the packs go in frozen.
Measure your own time like this:
- Load the carrier with the real payload; do not test it empty.
- Put the logger next to the product, not under the lid.
- Run the round under normal conditions and open the lid as often as a real delivery would.
- Repeat in summer and winter, and keep the dated record.
