Dear colleagues,

I would appreciate guidance and practical experience regarding holdover time for vaccines stored in a walk-in cooler following a power failure or refrigeration system breakdown.

Specifically, I am interested in the recommended approach for:

• Pentavalent vaccine
• DTP vaccine
• IPV vaccine
• Pneumococcal conjugate vaccine (PCV)

In particular:

How should the maximum allowable holdover time be determined when the walk-in cooler loses power?

Should vaccine-specific stability data be used, or should decisions be based primarily on the maximum/minimum temperature reached and duration of exposure?

What is the recommended procedure when the temperature remains within +2°C to +8°C during the power interruption?

What should be done if the temperature exceeds +8°C but remains below the vaccine-specific heat stability limit?

Which WHO/UNICEF/EVM guidance or technical documents can be used to support these decisions?

I would particularly appreciate examples from countries or programmes using walk-in cold rooms for routine EPI vaccine storage.Thank you for sharing your technical guidance and field experience.

Dear Mohamed

We have two refrigerated warehouses measuring 8m in height and 21m in depth, with widths of 16m and 9m respectively. We have 600 storage positions (sized 2.0m high x 1.20m long x 1.20m wide) and 3.0m-wide aisles for electric forklifts. There is also a designated area for vaccine containers arriving from the manufacturer, allowing them to be opened under controlled conditions. Order picking and packaging are likewise carried out in these spaces at temperatures between 2ºC and 8ºC.

How should the maximum permissible holding time be determined in the event of a power outage in a walk-in cold room?

Operational qualification and performance qualification are conducted; the former is performed with the cold room empty, and the latter with the vaccines inside. Measurements are taken using backup equipment and then with the primary systems. Temperature sensors are placed at various heights—corresponding to where the vaccines will be stored—and across the depth and width of the cold room, specifically on the shelving units rather than in the transit aisles.

Should stability data specific to each vaccine be used, or should decisions be based primarily on the maximum and minimum temperatures reached and the duration of exposure?

Thermal stability data covering the product's entire shelf life (not at 6 months) and data from temperature excursion tests for each vaccine are required. While manufacturers do not always provide this specific data directly, they do supply the Vaccine Vial Monitor (VVM), which serves as a guide.

What is the recommended procedure when the temperature remains between +2°C and +8°C during a power outage?

The contingency plan must be followed. This involves a communication chain covering the electricity provider (regarding outage duration), the backup generator (investigating why it is not running), transport services, the backup storage facility, etc.

What measures should be taken if the temperature exceeds +8°C but remains below the vaccine's specific thermal stability limit?

Each manufacturer specifies this in the product insert.

Best regards.