Probably the biggest difference is that a vaccine fridge has a micro-processor (like a computer) controlling it. It determines when the fridge compressor should turn on and off. A domestic fridge has a dial that turns the compressor on, and no control over when it should turn off.
The next big difference is that a vaccine fridge is fan forced. This ensures a more even temperature distribution throughout the fridge. This is similar to a fan forced oven. Over stocking a fridge will compromise this and the reason why you should buy a larger fridge if possible.
The built-in processor offers extra capabilities as well. Displaying the temperature on the outside of the fridge allows staff to check what is going on. This is an expensive thermometer but it is critical that staff are aware of the temperature sensitivity of the vaccines.
The vaccine fridge will also have a number of alarm options. This will include a local buzzer or siren, but can also include external alarm capabilities. So if the door is left open then staff will be quickly notified. In a domestic fridge there are no alarms and it isn’t until the next person uses the fridge that the problem is found.
One feature that I feel is important is a non-exposed cooling plate. Not all vaccine fridges have it, and it makes it possible for product to be pushed against the cooling plate.
Glass doors are also an optional feature. Some people like them because it means the door doesn’t have to be held open, but it does impact on the fridge’s ability to retain heat if power is lost.