Can chemistry thaw the vaccine cold chain?

Excerpts of an article featured on Chemistry World publication, 19th January 2021; click here to read the full article.

As the world celebrates the arrival of vaccines to protect against Covid-19, the logistics of distributing them is under the spotlight as never before. It’s a delicate balancing act – both heat and excessive cold damage vaccines. Keeping vaccines at just the right temperature to ensure they’re effective is an expensive business, with the cold chain accounting for up to 80% of the costs of delivery.

‘The agencies responsible for taking vaccines to the developing world spend more than $400 million [£290 million] a year just on refrigerators – just keeping the cold chain intact. That in itself would buy a lot of vaccines,’ says Bruce Roser, a biomedical researcher who works on vaccine stabilisation at the company he founded, Stablepharma, in the UK. 

Bruce Roser’s journey began with the resurrection plant – so named because it can survive without water, almost completely desiccated. This is thanks to its capacity to make a sugar – trehalose – that protects the plant as it dries out. When water is available the plant unfolds and begins to grow again. ‘Trehalose turns out to be the ideal stabilising agent for long-term high temperature storage of pretty well anything,’ says Roser. ‘Most of the things that the pharmaceutical industry has used to stabilise products during the drying process, including other sugars, break down eventually and react with the products and damage them. But trehalose doesn’t do that.’ It’s also inert in the body. It’s already being used as the stabilising agent in more than 25 pharmaceuticals.

In Stablepharma’s system, called StablevaX, the manufacturer’s liquid vaccine is added to a proprietary buffer containing the sugar and the solution loaded into a sponge. The wet sponge goes into a syringe and is dried. Unlike other sugars, trehalose doesn’t crystalise but gets gradually more viscous until it becomes a clear solid.

‘The product, including the molecules that could gradually damage it in storage, like oxygen or other chemicals, is trapped in a completely inert, transparent, soluble glass,’ Roser explains. ‘You’ve stopped chemistry … and everything is frozen in time and in space. When you add water, the whole process just goes into reverse, and the molecule ends up as it was when you started.’

Bruce Roser identified that the resurrection plant survives droughts thanks to a stabilising sugar called trehalose

Roser’s company has worked on around 90 vaccines that can be stabilised using this technique, and is now looking at those for coronavirus. He’s confident that mRNA can also be stabilised, but more challenging will be the lipid nanoparticles that surround it. However, his company is talking to the vaccine manufacturers about what could potentially be a second generation of vaccines against Covid-19. 

The urgency of tackling Covid-19 may have come too early for these advances, but their developers hope they’ll eventually help to put vaccines on shelves around the world for use whenever they’re needed.