Cold boxes and vaccine carriers
A cold box is a large insulated container lined with coolant packs, used to collect and transport vaccine supplies between stores and as emergency storage when a refrigerator breaks down. A vaccine carrier is a smaller insulated box for taking vaccines to a session. India's handbook describes small (5–8 litre) and large (20–22 litre) cold boxes in the programme, with hold-over measured in days when the lid stays shut.
WHO's PQS catalogue has separate categories for cold boxes and vaccine carriers (E004) and coolant packs (E005), which is useful when a funder specifies prequalified equipment.
Why ice packs must be conditioned
Ice packs come out of a deep freezer at well below 0 °C — the programme freezes them at −15 to −25 °C. Placed straight into a box against vials, they chill the contents below freezing. The handbook reports that unconditioned packs can drop the inside of a vaccine carrier below zero within 10–20 minutes, enough to damage freeze-sensitive vaccines such as Hepatitis B, DPT, Pentavalent, IPV and TT.
Conditioning simply lets the pack warm until its ice is at about 0 °C throughout, so it can cool without freezing.
How conditioning works in practice
- Take frozen packs out of the freezer and close the freezer door.
- Lay them out at room temperature with space around each pack — the handbook suggests about 5 cm.
- Wait until beads of water cover the surface and you hear water slosh when the pack is shaken.
- Only then load them into the cold box or carrier.
- In a hot Indian room this happens faster; in winter it takes longer — judge by the signs, not the clock.
Packing a cold box
| Step | Principle |
|---|---|
| Line the box | Conditioned packs at the bottom and sides, as shown on the lid diagram |
| Load products | Vaccines and diluents in cartons or bags; a thermometer inside if possible |
| Protect freeze-sensitive vials | Never in direct contact with packs; use spacers or packing material |
| Top layer | A row of packs on top, covered with a plastic sheet, then close securely |
| During use | Keep the lid shut; don't stack weights on it; keep the rubber seal in place |
Beyond vaccines
The same physics applies to insulin deliveries, biologics, diagnostic reagents and blood samples. Pharmacies and labs that send or receive cold parcels should use packs conditioned for the product's range, qualified boxes where their customers require them, and a temperature indicator or logger inside. WHO's technical supplements on storage and transport cover qualifying shipping containers and transport monitoring for those who need a formal system.
Common mistakes
- Packing straight from the freezer to save time on a busy session morning.
- Letting freeze-sensitive vials rest directly against a pack because the box is too small for spacers.
- Opening the lid repeatedly to show or count stock, which drains hold-over far faster than the box's rating suggests.
- Using one cold box both for the day's stock and as a store for spare frozen packs.
Tips for Indian conditions
- Keep cold boxes out of direct sun in vehicles and at session sites; shade alone extends hold-over noticeably.
- Have enough frozen packs ready before a campaign or a forecast outage; a vaccine-storing freezer should not be used to freeze large batches of new packs.
- Clean and dry boxes after use and check seals and hinges; a cracked lid ruins hold-over.
- Record the time products left the fridge and when they returned.
Frequently asked questions
- How do I know an ice pack is conditioned?
- India's cold chain handbook uses two signs: water beads on the surface ('sweating') and the sound of liquid water when you shake the pack.
- Can I use gel packs from the kitchen freezer?
- Kitchen packs are not designed or tested for vaccine transport, and a household freezer may freeze them very cold. Use the coolant packs your programme or supplier specifies and condition them before use.
