Dry ice may have been around since the 1920s but it is currently a hotter topic than ever before. As healthcare providers prepare to distribute the vaccines they hope will put an end to the COVID-19 pandemic, dry ice is emerging as an unlikely hero in the all-important supply chain in the battle against COVID-19.
Depending on the temperature and pressure, carbon dioxide (CO2) exists in three states – as a gas, liquid or solid. Essentially, dry ice is solid carbon dioxide.
It is made by reducing the pressure and temperature of liquid CO2 till it converts into a clean, white snow. This snow can then be compressed under high pressure to form blocks, slices and pellets.
Because dry ice has no taste or smell, is non-poisonous and non-flammable, it is a highly effective cooling and freezing agent. It is particularly convenient for in-transit cooling, where power supply can be an issue.
Vaccines need a good chill
When it comes to COVID-19 vaccines, Pfizer-BioNTech and Moderna are leading the charge. In early December, the Pfizer-BioNTech vaccine became the first to be approved for use in the US and the UK and, on 8 December, a 90-year-old British woman became the first person in the world to receive it.
Whereas Moderna’s vaccine is able to survive in temperatures ranging from 2 to 8 degrees Celsius for up to 30 days, the Pfizer vaccine is trickier to handle, since it requires more advanced refrigeration. In order for the vaccine to remain stable, it has to be stored at sub-Arctic temperatures – or at minus 70 degrees Celsius to be more precise. That is about 50 degrees colder than any other vaccine currently in use.
Dry ice is by no means a newfangled technology trend. The properties of solid carbon dioxide were first discovered in the early twentieth century and dry ice has been produced commercially since the 1920s. However, in 2021, it is set to become cooler than ever, with sales reported to have risen sharply after Pfizer announced the encouraging results for its COVID-19 vaccine candidate.
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“When I first heard about the temperature requirements of the Pfizer-BioNTech vaccine, my immediate was ‘they have to use dry ice!’,” says Flemming Kay, Market Manager Food and resident dry ice expert at Linde in Denmark.
Many usage areas for dry ice
Dry ice is used extensively in the food industry for freezing and cooling to keep produce fresh in transit, and in the medical field for transporting and storing fragile materials such as blood, tissues and bio samples. The main advantages of dry ice are that it maintains a constant, lower temperature than that of water ice and does not create any mess or leave any residue, other than incidental frost from moisture in the atmosphere.
“Another option would be to keep the vaccine cool using liquid nitrogen – but it is more costly, more complicated to distribute, and significantly riskier for the people handling it, since its temperature is minus 190 degrees Celsius,” Kay continues, adding: “Dry ice maintains a constant temperature of minus 79, which is handy considering the requirement for the Pfizer vaccine is minus 70.”
Based on current projections, Pfizer says its and BioNTech’s combined production capability have the potential to supply up to 1.3 billion doses of the vaccine by the end of next year.
Or, as Flemming Kay observes: “That’s a lot of dry ice”.
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Text: Isabel Klieger