Vaccines are usually stored between +2°C and +8°C.

So why does everyone keep talking about 5°C?

The answer is simple: 5°C sits in the middle.

Australia’s National Vaccine Storage Guidelines: Strive for 5 explains that “Strive for 5” refers to 5°C, the midpoint between +2°C and +8°C, which is the recommended storage range for most vaccines. Many vaccines can be damaged or destroyed outside this range.

But there is a bit more to it than maths.

The 5°C target gives you breathing room.

If your fridge is sitting around 5°C and the temperature drifts slightly, you still have space before it becomes too cold or too warm. If it drops a little, you are still above +2°C. If it rises a little, you are still below +8°C.

That buffer matters.

The safe range is not very wide

A vaccine fridge does not have much room for error.

Below +2°C is too cold. Above +8°C is too warm. The Australian Government’s vaccine fridge temperature chart says temperatures should be checked twice a day, in the morning and afternoon, and recorded as current, minimum and maximum readings. It also identifies +2°C to +8°C as the correct range.

That means the full working range is only six degrees wide.

For a household fridge, six degrees might not sound like much. For vaccines, it is everything.

If a fridge is running at 3°C, it may look like it is “in range”, but it only has a small buffer before it becomes too cold. If there is a cold spot at the back of the fridge, or the vaccine is near a cooling plate or air outlet, some stock may be exposed to temperatures colder than the display suggests.

If a fridge is running at 7°C, it is also technically in range, but there is very little room left before it becomes a warm breach.

That is why 5°C is the sweet spot.

5°C protects against both ends of the problem

When vaccine storage goes wrong, people often worry about the fridge getting too warm.

That is understandable. Heat can damage vaccines.

But freezing can be just as serious, and in some cases worse. Some vaccines, especially aluminium-adjuvanted vaccines, can be permanently damaged by freezing. The problem is that freeze damage may not be obvious just by looking at the vial.

So the goal is not “keep vaccines as cold as possible”.

The goal is “keep vaccines cold enough, but not too cold”.

That is the real point of Strive for 5.

Why the history matters

The 5°C target also makes sense when you remember how vaccine storage used to be managed.

Historically, many vaccines were stored in domestic or non-dedicated fridges. These fridges were designed for food, not vaccines. They had warm spots, cold spots, door temperature swings and defrost cycles. Some older guidance and cold chain material also relied on daily manual temperature readings using digital, electronic or mercury/maximum thermometers.

In that world, +2°C was not a comfortable target. It was too close to 0°C.

A thermometer could be slightly inaccurate. The person checking it might only read it once or twice a day. The fridge might cycle colder overnight. Vaccines near the back wall or cold plate might be colder than the air temperature being recorded.

So aiming for 5°C made practical sense.

It kept vaccines away from freezing while still leaving room before the fridge became too warm.

Modern vaccine fridges are better, but the buffer still matters

Today, vaccine storage has improved.

Current Australian guidance says vaccines should be stored in purpose-built vaccine refrigerators. Domestic refrigerators, including bar fridges, commercial fridges and industrial fridges, are not designed for vaccine storage and must not be used because they have a propensity to freeze vaccines.

The RACGP also says purpose-built vaccine refrigerators are the only type recommended for storing vaccines, and warns against cyclic defrost and bar refrigerators because their internal temperatures fluctuate considerably.

Modern systems also use better monitoring. NSW Health, for example, requires immunisation products to be stored in a purpose-built vaccine refrigerator with continual data logging, while still requiring current, minimum and maximum temperatures to be manually recorded twice daily.

So yes, the equipment is better.

But the reason for 5°C has not gone away.

Even with a good vaccine fridge and a data logger, the temperature inside the fridge is not perfectly flat. Door openings, stock deliveries, air movement, fridge load, probe position and room temperature can all affect what happens.

A stable fridge running around 5°C is still safer than one hovering near the edge.

5°C is not a magic number

It is worth saying this clearly.

5°C is not magic.

A vaccine stored at 4.8°C is not “better” than one stored at 5.2°C. The real requirement is that vaccines remain within the approved range.

But 5°C is useful because it gives staff a clear target.

It is easy to remember.

It is easy to explain.

It gives a practical safety margin between too cold and too warm.

What staff should look for

A vaccine fridge sitting around 5°C is usually a good sign, but it is not the only thing to check.

Staff should still look at the current temperature, the minimum temperature and the maximum temperature. They should reset the min–max display after recording, check the logger data when required, and respond quickly if the temperature goes outside range.

The Australian Government temperature chart says that if the temperature is out of range, vaccines should be kept in the purpose-built vaccine refrigerator, labelled Do not use / Do not discard, and advice should be sought.

The number on the screen is only part of the story.

The trend matters.

The minimum and maximum matter.

The location of the stock matters.

The response matters.

Key takeaway

Vaccine fridges are set to 5°C because it is the safest target in the middle of the recommended +2°C to +8°C range.

It gives you a buffer against freezing at one end and heat exposure at the other.

That buffer mattered in the days of domestic fridges and manual thermometers, and it still matters now, even with purpose-built vaccine refrigerators and data loggers.

Strive for 5 is not just about hitting a number.

It is about giving vaccines the best chance of staying safely in range.