British scientists have found a way of keeping vaccines stable without refrigeration, a discovery which they say could transform immunisation campaigns in the developing world.

One of the biggest costs of immunising children in poor countries is keeping the vaccines cool.

Now researchers from Oxford University say they have worked out how to do that cheaply and simply - just by adding sugar.

Professor Trevor Duke, from the Centre for International Child Health in Melbourne, has spent years taking part in vaccination programs in the Asia-Pacific.

He has only just returned from Papua New Guinea and says he has seen first-hand just how difficult it is to keep vaccines cool.

"People live many, many hours and sometimes days away from a health centre that has vaccines," he said.

"Many of the smaller health centres in rural areas aren't able to have refrigerators because they don't have electricity, and so what generally happens is that health workers travel from a central site to a preferable remote rural area with vaccines if they're going to deliver them.

"That takes time and it also takes cold chain equipment, so it takes eskies or ice boxes and they're quite heavy.

"So generally speaking only one day's worth of vaccines can be taken at any time."

Professor Duke says almost all vaccines spoil if they get hotter than about 4 degrees Celsius.

"Particularly the live vaccines and particularly measles vaccines [spoil]," he said.

"Problems with the cold chain have been reasons why even if children receive a measles vaccine in some tropical developing countries it may not be effective if the vaccine's been exposed to heat before its administration."

But he is hopeful those problems could soon be a thing of the past.

Fridge-free vaccines

Scientists from Oxford say they have worked out how to store two different virus-based vaccines for up to six months at 45 degrees Celsius, or a year at 37 degrees.

A team lead by Dr Matt Cottingham mixed the vaccines with two types of sugar then left it to dry out on a filter.

The mixture turned into a syrup, which solidified on the membrane.

When the membrane was flushed with water, the vaccine was reanimated with only a tiny reduction in quality.

Professor Duke says this could go a long way to cutting the costs of vaccination.

"The cold chain's extremely expensive," he said.

"I know, for example, in Papua New Guinea when we're considering the introduction of a new vaccine, the cold chain equipment has to be revived and there has to be a lot more of it if you're going to be able to store a new vaccine.

"In Papua New Guinea in 2008 the haemophilus influenzae vaccine was introduced and that required a substantial upgrading of the cold chain equipment at quite large costs."

The World Health Organisation estimates that the logistics of keeping vaccines cool costs up to $US200 million a year, which makes immunisation about 20 per cent more expensive.

Dr Cottingham says people could now transport vaccines to remote areas equipped with merely a bicycle and a backpack.

And Professor Duke says the implications go even further.

"It may be possible to store vaccines in remote health facilities that don't have refrigerators and then deliver them to nearby villages everyday of the week rather than once every three months, which is currently often what happens," he said.

"There's probably even greater potential than just someone on a bicycle with a backpack; a large delivery of vaccines for communities for extended periods of time."

The research has just been published in the journal Science Translational Medicine.