Every cabinet has warmer and colder zones
Cold air is heavier than warm air and flows from the evaporator or fan outlet across the cabinet. Spots near the outlet, the back wall or the bottom of a chest run colder. Spots near the door, the top of an upright cabinet or anywhere air can't circulate run warmer and swing more.
A good cabinet narrows these differences but never removes them entirely. Temperature mapping, where it has been done, shows exactly where the zones are in your unit.
Upright refrigerators
- Use the middle shelves for vaccines. The CDC recommends keeping vaccines and diluents 2 to 3 inches (about 5 to 7.5 cm) from the walls, ceiling, floor and door.
- Never use door shelves, crisper drawers or deli drawers — the CDC lists these among the least stable parts of a household-style fridge.
- Avoid the shelf directly under a cooling vent, where vaccines can freeze.
- Leave space between boxes and rows so air can move; don't pack the cabinet solid.
- Keep vaccines in their original cartons, each type in its own labelled container.
Top-opening ice-lined refrigerators
In a chest-style ILR the logic flips: the bottom is the coldest part because cold air settles. India's Handbook for Vaccine and Cold Chain Handlers tells handlers to keep all vaccines in the basket supplied with the ILR — never on the floor — with freeze-sensitive vaccines in the upper part and vaccines that tolerate cold better lower down.
If the basket is missing, the handbook suggests two layers of empty ice packs laid flat on the floor as a barrier. A thermometer or probe goes in the basket among the vaccines.
Safe and unsafe positions at a glance
| Position | Upright fridge | Top-opening ILR |
|---|---|---|
| Middle of cabinet, among other stock | Preferred | Preferred, inside the basket |
| Near cooling outlet or back wall | Avoid — freeze risk | Avoid contact with lining |
| Cabinet floor | Avoid | Never — coldest zone |
| Door shelves | Never | Not applicable |
| Top of cabinet | Usable if mapping shows it stable | Freeze-sensitive vaccines in upper basket |
| Crisper or deli drawers | Never | Not applicable |
Organising stock for fewer errors
- Earliest expiry in front (or on top in a chest), so it is used first.
- Similar-looking products, and paediatric and adult versions of the same vaccine, on different shelves.
- Diluents with their matching vaccine where the label allows — never in a freezer.
- Other medicines in separate, clearly marked containers; no food or drinks in the unit.
- Shelf labels showing what goes where, so a relief staff member doesn't guess.
Where the monitoring probe goes
Place the buffered probe of the data logger in the centre of the vaccines, not against a wall or near the door. The CDC notes that a probe near the walls, floor, vent, ceiling or door may read warmer or colder than the vaccines themselves. Some purpose-built units specify a probe position — follow it.
Keep the logger display outside so staff can read it without opening the door.
Water bottles and thermal ballast
Older advice often suggested filling empty space with water bottles to steady the temperature. The CDC now says water bottles are not recommended for most pharmaceutical-grade and purpose-built units — follow the manufacturer's guidance. In a household-style fridge, bottles on the floor and door may still help, but they must never crowd vaccines or block airflow.
Frequently asked questions
- Is the top shelf of a fridge safe for vaccines?
- It depends on the cabinet. In a household fridge it may sit under a cooling vent and risk freezing. In a fan-forced pharmaceutical unit it may be fine. Mapping data or the manufacturer's manual is the best guide.
- Why can't vaccines go on the floor of an ILR?
- Cold air settles at the bottom of a chest-style ILR, so the floor is the coldest point and can freeze freeze-sensitive vaccines. India's programme guidance keeps all vaccines in the basket.
