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The world's first ready-to-use vaccines requiring no refrigeration are due to be tested in clinical trials in India. If successful, the heat-stable vaccines could mean that millions more children in developing countries are immunised against diseases such as hepatitis B and whooping cough.

Currently, almost half of all vaccine supplies are wasted, mostly because of interruption of the 'cold chain' — the continuous refrigeration needed between manufacture and immunisation. This can happen, for example, through faulty storage in airports or health centres, or because of delays caused by vehicle breakdowns.

But a UK pharmaceutical company, Cambridge Biostability (CBL) has developed 'next generation' heat-stable vaccines that do not need the costly cold-chain. CBL has teamed up with an Indian drug company, Panacea Biotec, who will make and test the vaccines' effectiveness in people.

The technology is based on a natural process called 'anhydrobiosis'. Some plants and microscopic animals use this process to survive in a 'dried-out' state of suspended animation for years by turning a sugar into a syrup solution, which then hardens into chemically inert 'glass'.

With this in mind, researchers spray-dried a vaccine with a sugar solution to create solid glass spheres. The spheres are then suspended in an inert liquid such as a perfluorocarbone, which is chemically stable, eliminating the need for refrigeration. Though the spheres are insoluble in the suspension, upon injection they dissolve in the body to release the vaccine.

According to John Lloyd of the Children's Vaccine Programme "stable vaccine technology means that we can get out to more children in countries where immunisation coverage is only at 50 per cent. We can reach 100 per cent".

Although freeze-dried vaccines can also eliminate the cold-chain, they still need to be reconstituted before use, and vaccines are often destroyed by the addition of contaminated water or diluting to the wrong concentrations. Stable liquid vaccines avoid this problem by being ready to inject from the start.

Bruce Roser, chief scientist at CBL, told a press conference yesterday (October 19) that vaccines giving protection against many diseases in one shot are desirable because mothers are often reluctant or unable to bring their children back to clinics repeatedly. But combining multiple vaccines into one dose can be difficult because of chemical interactions between active ingredients. The inert nature of the stable liquid vaccine, said Roser, means that more vaccines could be packed into one injection.

The new vaccine also has the potential for 'slow release', which would reduce the need for booster doses. The vaccine has the backing of the World Health Organisation and the Global Alliance for Vaccines and Immunisation, but despite the excitement surrounding the technology, so far, it has been tested only in mice and guinea pigs.

Panacea Biotec will be testing the new technique with a pentavalent vaccine — designed to work against diphtheria, whooping cough, tetanus, hepatitis B and meningitis-causing Haemophilus influenzae B — in clinical trials in India during the next three years. 

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