WHO-Endorsed Passive Cooling Methods: What Are They and How Do They Work?

Quick answer

WHO-endorsed passive cooling methods keep vaccines at safe temperatures (2°C–8°C) without electricity. These techniques use insulated containers, phase-change materials (PCMs), and evaporative cooling to protect vaccines during transport and storage in remote areas. They’re low-cost, durable, and designed for health workers with limited resources. Proper training and monitoring ensure vaccines stay effective until they reach patients.

If you’re a health worker in a remote setting, you’ll need practical guidance on choosing and using these methods. Our ebook, Keep Vaccines Potent Without a Fridge: WHO-Endorsed Passive Cooling Methods for Remote Health Workers, walks you through each step, from setup to troubleshooting.

Why passive cooling matters for vaccines

Vaccines lose potency if they get too hot or too cold. In remote areas, electricity is often unreliable or unavailable, making refrigeration impossible. Passive cooling methods solve this problem by maintaining a stable temperature range (2°C–8°C) without power. These methods are endorsed by the WHO because they’re:

• Affordable: Low upfront and maintenance costs.
• Durable: Built to withstand rough transport and extreme weather.
• Simple: Designed for health workers with minimal training.
• Reliable: Proven to work in real-world conditions.

Without passive cooling, vaccines can spoil during transport or storage, wasting resources and leaving communities vulnerable to preventable diseases.

WHO-approved passive cooling techniques

1. Insulated containers with ice packs

The most common method uses a well-insulated box or carrier, like a vaccine transport box or cold box, paired with frozen ice packs. Here’s how it works:

• Insulation: The container’s walls are made of materials like polyurethane foam or vacuum panels, which slow heat transfer.
• Ice packs: Frozen water or gel packs are placed around the vaccines to absorb heat. As they thaw, they release cold air, keeping the interior cool.
• Temperature monitoring: A thermometer or temperature logger tracks the internal temperature to ensure it stays within the safe range.

This method is ideal for short-term transport (up to 48 hours) or temporary storage. However, it requires access to freezing facilities to prepare the ice packs.

2. Phase-change materials (PCMs)

PCMs are substances that absorb or release heat as they change from solid to liquid (or vice versa). For vaccine cooling, PCMs are designed to melt at 5°C, maintaining a stable temperature around the vaccines. Here’s why they’re useful:

• Longer cooling: PCMs can keep vaccines cool for days, even in hot climates.
• No freezing needed: Unlike ice packs, PCMs don’t require freezing. They’re pre-conditioned to melt at the right temperature.
• Reusable: Once melted, PCMs can be re-frozen and reused.

PCMs are often used in vaccine carriers or cold boxes. They’re especially valuable in areas where freezing facilities are scarce or unreliable.

3. Evaporative cooling

Evaporative cooling uses the natural process of water evaporation to lower temperatures. It’s simple, low-cost, and effective in dry climates. Here’s how it works:

• Setup: A porous clay pot or container is filled with water. Vaccines are placed inside a smaller, sealed container within the larger pot.
• Evaporation: As water evaporates from the outer pot, it draws heat away from the inner container, cooling the vaccines.
• Humidity control: A damp cloth or lid helps regulate evaporation to maintain the right temperature.

This method is best for short-term storage (up to 24 hours) in hot, dry environments. It’s not suitable for humid climates, where evaporation is less effective.

Choosing the right method for your setting

Not all passive cooling methods work in every situation. The best choice depends on factors like climate, transport time, and available resources. Use this table to compare the three WHO-approved methods:

If you’re unsure which method to use, consider the following:

• Transport time: For trips longer than 48 hours, PCMs are the best choice.
• Climate: Evaporative cooling only works in dry areas. In humid or variable climates, use insulated containers or PCMs.
• Resources: If freezing facilities are unavailable, PCMs or evaporative cooling may be your only options.

Step-by-step: Setting up passive cooling

Here’s how to set up each method safely and effectively.

Insulated containers with ice packs

1. Prepare the ice packs: Freeze the ice packs for at least 24 hours before use. Ensure they’re fully frozen to maximize cooling time.
2. Condition the container: Pre-cool the insulated container by placing it in a cool environment (e.g., a shaded area) for a few hours.
3. Load the vaccines: Place the vaccines in the center of the container, surrounded by the frozen ice packs. Avoid direct contact between vaccines and ice packs to prevent freezing.
4. Monitor temperature: Use a thermometer to check the internal temperature regularly. If the temperature rises above 8°C, add more ice packs or replace the existing ones.
5. Seal the container: Close the container tightly to minimize heat transfer.

Phase-change materials (PCMs)

1. Pre-condition the PCMs: If the PCMs are frozen, allow them to thaw to 5°C before use. If they’re already at 5°C, they’re ready to go.
2. Load the container: Place the PCMs around the vaccines in the insulated container. Ensure the vaccines are not in direct contact with the PCMs.
3. Monitor temperature: Use a thermometer to track the temperature. PCMs should maintain a stable 5°C environment.
4. Re-freeze PCMs: After use, re-freeze the PCMs for future use. This may require access to a freezer or cold chain facility.

Evaporative cooling

1. Prepare the outer pot: Fill a porous clay pot or container with water. The pot should be large enough to hold a smaller, sealed container for the vaccines.
2. Load the vaccines: Place the vaccines in the smaller, sealed container and position it inside the larger pot.
3. Cover the setup: Use a damp cloth or lid to cover the outer pot. This helps regulate evaporation and maintain humidity.
4. Monitor temperature: Check the temperature regularly. If the water in the outer pot evaporates too quickly, add more water to maintain cooling.
5. Store in a dry area: Keep the setup in a shaded, dry location to maximize evaporation.

Common challenges and how to solve them

Even with the best methods, passive cooling can go wrong. Here’s how to troubleshoot common issues:

If you’re facing persistent issues, our ebook, Keep Vaccines Potent Without a Fridge: WHO-Endorsed Passive Cooling Methods for Remote Health Workers, provides detailed troubleshooting guides and field-tested solutions.

Who should use this ebook?

This ebook is designed for health workers, logisticians, and program managers who:

• Work in remote or off-grid areas with unreliable electricity.
• Need to transport or store vaccines without access to refrigeration.
• Want step-by-step guidance on setting up and maintaining passive cooling systems.
• Need to train staff or volunteers on WHO-approved cooling methods.
• Are looking for cost-effective, durable solutions to keep vaccines potent.

Whether you’re a community health worker, a nurse in a rural clinic, or a program manager overseeing vaccine distribution, this ebook gives you the tools to implement passive cooling safely and effectively. Get your copy today and ensure your vaccines stay potent, no matter where you work.

Frequently asked questions

What is the difference between active and passive cooling for vaccines?

Active cooling uses electricity-powered devices like refrigerators or freezers to maintain vaccine temperatures. Passive cooling relies on insulated containers, phase-change materials, or evaporative cooling to keep vaccines cool without power. Passive methods are ideal for remote or off-grid settings where electricity is unreliable or unavailable.

How long can vaccines stay cool with passive cooling methods?

It depends on the method and conditions. Insulated containers with ice packs can keep vaccines cool for up to 48 hours. Phase-change materials (PCMs) can maintain temperatures for up to 5 days. Evaporative cooling is effective for up to 24 hours in dry climates. Always monitor the temperature to ensure vaccines stay within the safe range (2°C–8°C).

Can I use passive cooling for all types of vaccines?

Most vaccines can be stored using passive cooling methods, but some (e.g., oral polio vaccine) require freezing temperatures. Always check the vaccine manufacturer’s guidelines for specific storage requirements. Passive cooling is best suited for vaccines that need to be kept between 2°C and 8°C.

What are the biggest mistakes to avoid with passive cooling?

The most common mistakes include:

• Not pre-cooling the container before loading vaccines.
• Allowing vaccines to come into direct contact with ice packs or PCMs, which can cause freezing.
• Failing to monitor the temperature regularly.
• Using evaporative cooling in humid climates, where it’s ineffective.
• Not replacing or re-conditioning cooling materials (e.g., ice packs or PCMs) when needed.

How do I know if my passive cooling setup is working?

Use a thermometer or temperature logger to monitor the internal temperature of the container. Check the temperature at least every 4–6 hours. If the temperature rises above 8°C or falls below 2°C, take corrective action (e.g., replace ice packs, add water to evaporative cooling setup).

Is passive cooling safe for vaccines during air transport?

Yes, passive cooling is safe for air transport, but you must follow airline regulations for carrying dry ice or other cooling materials. Insulated containers with PCMs are often the best choice for air transport because they don’t require freezing and can maintain temperatures for longer periods. Always check with the airline for specific requirements.

Final thoughts

Passive cooling methods are a lifeline for health workers in remote areas, ensuring vaccines stay potent without electricity. By choosing the right method for your setting and following best practices, you can protect vaccines from spoilage and keep communities safe.

If you’re ready to implement these methods in your work, our ebook, Keep Vaccines Potent Without a Fridge: WHO-Endorsed Passive Cooling Methods for Remote Health Workers, provides everything you need to get started. From step-by-step setup guides to troubleshooting tips, it’s your go-to resource for keeping vaccines effective in any setting.