We have a covid-19 vaccine that works. But can we keep it cold enough to get it to enough people? Among Pfizer and BioNTech’s long , which this week was reported to be 90 per cent effective, is the challenge of its “ultra-low temperature formulation”, and how to store and distribute it along the so-called “cold chain”.
Between manufacture and doses being given to people, the vaccine needs to be kept frozen at about -70°C, around four times colder than a home freezer can manage. Once it has left Pfizer’s manufacturing facilities in Kalamazoo, Michigan, and Puurs, Belgium, the vaccine cannot be thawed and frozen more than four times in transit, . He said that adds “another tricksiness” to logistics.
The vaccine, developed using a new approach of using messenger RNA from the coronavirus, is unusual in needing such low temperatures. Most vaccines are refrigerated at around 2-8°C, rather than frozen. Even those that are frozen, such as the Varivax vaccine used against the virus that causes chickenpox, are stored at much higher temperatures than Pfizer’s one.
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Nilay Shah at Imperial College London says healthcare systems have some experience of handling cells and samples at temperatures at around -70°C. However, he says it is “not at the volumes we anticipate for vaccines”.
Pfizer told żěè¶ĚĘÓƵ it is confident it can distribute the vaccine at such low temperatures. Vials of the vaccine will be put in purpose-built packaging about the size of an aircraft carry-on suitcase, weighing around 32 kilograms. Dry ice will be used inside to keep temperatures at -75°C, give or take 15°C, for up to 10 days. The dry ice (solid carbon dioxide) will be replenished along the journey. One trade body has there is enough capacity to supply that dry ice, at least in the US and Canada.
Deliveries will either be driven directly from Kalamazoo and Puurs to wherever they are being used, or flown to major hubs for onward distribution. For the UK, that will mean lorries and vans via Dover, so avoiding traffic jams that have been predicted in the event of a no-deal Brexit will be vital.
“Vaccines are quite tricky beasts to transport,” says Michael Head at the University of Southampton, UK. The easy bit will be when the vaccine is on a lorry, but it will become harder to keep the vaccine cold enough at transitions, such as when it is moved into or out of freezers at distribution centres. Shah says ultra low-temperature freezer capacity is already being scaled up at transport and warehouse hubs, but international distribution will be “more complex”.
The delicate nature of the vaccine means that everything needs to be ready at its “point of use”, such as a doctor’s surgery. Once thawed and put in a fridge at 2-8°C, Pfizer says it will be stable for five days, or no more than 2 hours at room temperature. Penny Ward at the Faculty of Pharmaceutical Medicine in London says careful planning is needed so that healthcare teams have patients “ready to go” at vaccination sites.
Ultimately, keeping the vaccine at the right temperature will be a logistical headache but not an insurmountable one, especially for a country like the UK, says Head. And even if there is a need for more equipment such as low temperature freezers along the supply chain, it will be possible: “It’s such an important challenge that even if it’s expensive, cumbersome and time-consuming, it’s worth the effort to get the extra infrastructure in place.”
The picture may be different in hotter countries and those lacking this infrastructure. Keeping vaccines at such low temperatures “is extremely challenging or even impossible” in low and middle-income countries with hot, humid weather, according to a  by the UK’s Royal Society.
One way around that may be the water-removal process of lyophilisation, turning the vaccine into a powdered form, says Ward. Pfizer says it is considering the approach. Some countries may simply opt for alternative vaccines that don’t need to be kept so cold, should they become available. “Even if the Pfizer vaccine is 90 per cent effective, we may see other countries choosing other vaccine candidates even if they’re less effective, simply because the logistics will be much easier for them,” says Head.
