Is It Safe to Cool Water Packs and Vaccines Together?

Published by Marvin Espino on

ice packs in medical refrigerator

Is it safe to cool water packs and vaccines together in the same refrigerator? The World Health Organization (WHO) maintains that cooling water packs requires separate refrigerators. The reason is warm or cold water packs can affect the temperature of the vaccines. When vaccines’ temperature shifts from the acceptable range, it loses its immunization capability.

So to prevent this from happening, several immunization programs follow this guideline to the core. However, not all health centers have enough budget for an extra fridge. So they combine water packs and temperature-sensitive vaccines.

The truth is no studies have yet proven the negative effect of cooling both water packs and vaccines in the same refrigerator. The WHO stated this perhaps as precautionary measures because excursions are too expensive to deal with.

So to give light on this topic and provide evidence-based recommendations, Geneva Goldwood and Steven Diesburg measured the effect of cooling both materials in the same place. Did it lead to temperature excursions? And did excursions always lead to stability loss or vaccine wastage?  Here’s how they did  it:

How to measure vaccine temperature

The study incorporated two ways of measurement. First is the use of Vaccine Vial Monitoring (VVM). It is a heat-sensitive paper that indicates whether or not vaccines have undergone temperature excursions.

The World Health Organization (WHO) prequalified VVM to be used on all types of vaccines. VVMs have different levels based on the heat stability of the vaccines. VVM 2 is designated to vaccines that have the highest heat-sensitivity, then VVM7, VVM14, and lastly VVM30 for most heat-stable vaccines. More information on VVMs below:

types of vaccine vial monitors

The VVMs consist of a reference circle with a color-changing indicator dot inside. That indicator dot has an optical density (OD). And the lifetime of the VVM is defined as the time it takes for the OD of the indicator dot to match the OD of the reference circle, also considered the endpoint by the  WHO.

Another way of measurement is the Arrhenius equation. The lifetime of the VVM mentioned above is temperature-dependent, and there is an established relationship between temperature and lifetime of a specific VVM as stated in the Arrhenius equation:

 k = A * exp(-Ea  / RT)

There they are, two ways of measuring the life of the vaccines based on VVMs and a formula. The goal of this study was to understand the impact on vaccine life of cooling both warm water packs and vaccines in one refrigerator. VVM life is the proxy for vaccine life and the Arrhenius equation is to calculate for the VVM life.

The setup of vaccines and water packs

Since this is a controlled study, several setups have been made to ensure the reliability of the results. Here are the materials used:

Water packs – PQS-prequalified specifically Blowkings, model BK 6 from Mumbai, India. Before placing in refrigerators, these water packs are conditioned to 43°C, the hot zone temperature for prequalified cold chain equipment.

Vaccine vials – 10 ml in size, between 2°C to 8°C (36°C to 46°F), and are equipped with specific VVM depending on the heat stability of the vaccines.

Thermocouples – Each vaccine vial is instrumented with thermocouples or temperature sensors from OMEGA Engineering, Inc., 5SRTC-TT-T-36, Stamford, CT, USA.

Refrigerator – This fridge accommodates both vaccines and water packs and hence need to be PQS-prequalified. The model used is specifically from Blowkings, BK6, Mumbai, India.

Temperature collector – This device is responsible for logging the temperature data from the thermocouples. The researcher used the NI cDAQ-9172 chassis, 9211 thermocouple input module, NI SignalExpress software, National Instruments Corporation, Austin, TX, USA

Here’s the set-up: water packs at 43°C together with vaccine vials between 2°C and 8°C (36°C to 46°F) were placed into the refrigerator. The researcher measured the temperature of the vials for one month, rearranging the vials and water packs’ location in the fridge as well as varying their number per test. The test was done in duplicate and triplicate, and each test contained up to 18 instrumented vials. Here is the location and number of vials and water packs for each test:

testing vaccine vials with cool water packs
Source: Elsevier Ltd, Authors: Geneva Goldwood  and Steven Diesburg

The temperature logging started immediately after the water packs and vials have been placed. The NIcDAQ device collected temperatures at a rate of two samples per minute and only stopped when the vials and water packs reached at least 5°C.

What’s the result?

The result suggested that no vaccines were damaged from a single temperature excursion or from repeated exposures to warm water packs in the same refrigerator for a month. However, it is worth mentioning that vaccine life depends on its heat stability in short relative to the inherent stability of its accompanying VVM.

VVM2 are most likely to lose stability due to cyclic warming brought by the warm water packs. But the result really depends on the location of vaccines and water packs in a fridge that has phase-change material-lined floor and walls due to it being better at resisting warming of vials.

Overall, the practice of stacking vaccines and warm water packs in the same refrigerator would not cause any serious loss of vaccine stability. And while the distance and location of the two materials will have a small impact on the result, further research is necessary to establish safe ratios and measurement of vials and water packs in different refrigerators.

The researchers even go as far as recommending to cool warm water packs and vaccines together as long as there is enough space and power in the fridge. They consider it a beneficial practice in cold chain management. By maximizing the space of the available equipment, it could even lead to a smaller percentage of vaccines getting exposed to unacceptable temperatures, and even fewer expenses on electricity and materials.


Sure, separating vaccines and water packs can be a cautious way of preventing excursions. It’s ok if there’s a spare fridge, but if there’s none, it’s now recommended to use one fridge for both vaccines and water packs. After all, health centers only use water packs to travel vaccines over a distance. That seldom happens in small health centers where the immediate recipient is adjacent to the centers. So using an extra fridge specifically for water packs can be an unnecessary cost. For struggling immunization programs, the researchers’ recommendations can be a good way of minimizing expenses, and as long as both vaccines and water packs are properly placed, then it also prevents vaccine wastage in the long run.


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