VACCINES that can survive extreme heat and cold could help protect millions more children in poor countries. The key is a 鈥渟table-liquid鈥� technology, which could also be used to make vaccines against pandemic diseases that could be kept stockpiled for many years.
As much as $300 million a year is spent in poor countries on the 鈥渃old chain鈥� 鈥� keeping vaccines refrigerated. Despite this, nearly half of all vaccines are spoilt when they get too warm. The developer of the stable-liquid technology, Cambridge Biostability in the UK, says that preventing this waste will enable 10 million more children a year to receive vaccinations at no extra cost.
The key is encasing the vaccine鈥檚 ingredients in a sugary coat that preserves them at temperatures of up to 60 掳C. The coating is made of combinations of simple natural sugars, such as raffinose, and an amino acid, typically glutamine. 鈥淭hey form a completely transparent, spherical glass-like ball about 3 micrometres in diameter,鈥� says Bruce Roser, chief scientist at Cambridge Biostability.
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The balls are suspended in an inert liquid, a perfluorocarbon (famously used for liquid breathing), which prevents bacteria spoiling the vaccine. Calcium phosphate is also added to the balls to make them neutrally buoyant, stopping them floating to the surface or settling out.
The resulting vaccines can survive extreme heat and cold. 鈥淵ou can keep the vaccine in the glovebox of your Land Rover in the Sahara,鈥� Roser says. When injected, the sugary balls dissolve, releasing the active ingredients, and the perfluorocarbon is eventually exhaled.
This week Cambridge Biostability received 拢950,000 from the UK government to work together with Panacea Biotec in New Delhi to develop a heat-resistant combination vaccine against diphtheria, tetanus, whooping cough, a form of meningitis and hepatitis B. The company is also working with the US on producing vaccines against bioweapons that will remain effective even if kept stockpiled for many years.
鈥淵ou can keep the vaccine in the glovebox of your Land Rover in the Sahara desert鈥�
For combination vaccines, the technology has another advantage. Each component can be coated before being combined, ensuring they cannot interfere with each other as sometimes happens in conventional vaccines. The balls can also be made to dissolve at different rates, allowing booster doses normally given separately to be given in the same injection as the initial vaccine, for instance.
Roser鈥檚 aim is to produce a single heat-resistant vaccine against all 12 major childhood diseases targeted by the World Health Organization. The WHO says the stable-liquid approach is promising; its concern is whether the advantages outweigh the costs. These include funding clinical trials of any new vaccines as well as evaluating the safety of proposed alternatives to perfluorocarbon, whose use is undesirable because it damages the ozone layer. 鈥淪ometimes we must look beyond the technology and ask whether it will become too expensive,鈥� says Martin Friede, a vaccine specialist at the WHO.