As the UK became the first country in the world to approve Pfizer/BioNTech’s novel coronavirus vaccine, the hard work to overcome significant logistical hurdles began. Roger Mainwaring-Burton of Cambridge Consultants looks behind the glare of public attention to unravel the challenges of vaccine cooling.
Covid-19 storage
Following one of the most consequential scientific endeavours any of us can remember, three Covid vaccines emerged with promising preliminary results. But all bring with them vastly different storage and distribution challenges. The Pfizer/BioNTech jab, first to be announced and approved, has to be stored at -70°C (-94°F), the second by Moderna requires -20°C (-4°F) and the third by Oxford/AstraZeneca needs 4°C (39°F). There are relatively few methods of moving heat away from something to keep it cold, and which method is most appropriate varies, depending on the desired temperature, the surrounding environment, power availability and length of journey.
So what cooling systems are available for this crucial supply ‘cold chain’, and which are best suited to each vaccine? The three most common ways of moving heat are phase-change, mechanical and electrical (although mechanical is technically also phase-change). Phase-change includes ice (0°C), freezer blocks (0° – 8°C) and dry ice (-78.5°C). They can move a huge amount of energy, but they need recharging and can produce waste. The mechanical method is just like a conventional domestic refrigerator. A vapour compression (VC) system compresses a highly volatile refrigerant which flows around a circuit, moving the heat from a colder to a hotter place. Electrical uses thermoelectric coolers (TECs), where applying a voltage to a specific combination of metals causes heat to flow from one side to the other.