Most vaccines have to be frozen or refrigerated, which imposes major storage and transportation issues. Vaccines in freeze-dried form, on the other hand, can be stored at room temperature for several months.
The vaccination campaign against Covid-19 is a real challenge because of the drastic storage conditions of the vaccines. Pfizer’s vaccine must be stored at -60°C and Modern’s at -20°C. Even classic vaccines, such as those from AstraZeneca, must be refrigerated (between 2°C and 8°C). While this is not too much of a problem domestically, it is an obstacle to vaccination in many warm countries, which do not have the necessary infrastructure. According to the World Health Organization (WHO), half of the world’s vaccines are wasted every year due to poor storage and transportation conditions.
Soon the Sputnik V vaccine in freeze-dried form?
Researchers have been working for several years on the possibility of freeze-drying vaccines, which would allow them to be stored at room temperature for several months. Freeze-drying a product can produce a much more stable form that easy to move around. Last November, Russia announced that its Sputnik V vaccine would soon be available in powder form. If developed, this technique would give the vaccine a great advantage, especially for export to developing countries.
But the technique is actually very difficult to master. Freeze-drying damages components of the vaccine – such as the lipid membrane, proteins, and nucleic acids. Ice crystals can also form in the virus or cells, increasing the risk of protein aggregation. RNA vaccines, which require lipid nanoparticles, are therefore particularly sensitive to freeze-drying. However, adjuvants are available to avoid these drawbacks. Generally, saccharides and sugar alcohols are used, which stabilize proteins and prevent them from aggregating during the freezing phase. During the dehydration phase, these sugars replace the hydrogen bonds between water and proteins or phospholipids. In 2016, Australian researchers managed to develop a freeze-dried vaccine against seasonal flu using trehalose and glycine. Still using trehalose, another team managed to produce an RNA vaccine that can be stored for 10 months at 4°C.
Six months at room temperature
A new study published in Science Advances describes a novel approach in which the cell membrane, which is not resistant to dehydration, is removed to keep only the machinery of the cell inside. Once freeze-dried, the vaccine can be stored at room temperature for at least six months. Simply rehydrate with water at the time of administration. “Our system can reconstitute a dose of vaccine in less than an hour for one dollar,” says Michael Jewett, co-author of the study and a biochemist at Northwestern University. So far, the concept has only been tested with a conjugate vaccine, which combines the sugars of a bacterium with a specific protein. According to the authors, the advantage is that production can be decentralized and on-demand.
However, the production of freeze-dried vaccines would require a complete overhaul of the production chain. As of now during the current pandemic, this option is yet to be made available.