Scientists in Scotland have come up with a new way of making vaccines which they believe would prove especially useful in developing countries.
By Richard Black
BBC science correspondent
The idea is to use bacteriophages - viruses which live on bacteria but which are harmless to us - as a way of delivering a vaccine to the human body.
It is an attractive approach because bacteriophages are incredibly easy to grow and can multiply billions of times in hours.
An Indian child is vaccinated against polio
The research is in its early stages but experiments in mice have yielded some intriguing results.
Realising its potential could provide a way to protect children against many diseases with a single vaccine.
Cheap and easy
The World Health Organization's polio vaccination campaign has shown how successful a vaccine can be - so successful, in fact, that the disease could soon be no more than a memory.
But in many parts of the developing world, children routinely miss out on vaccines. That is partly because making vaccines is a complex process, beyond the facilities of some developing countries. The bacteriophage concept could be the answer.
Dr John March from the Moredun Research Institute near Edinburgh says it is very cheap to make the vaccine and very easy.
"At the moment, with most vaccines, you need very expensive tissue culture laboratories, trained personnel, very expensive reagents," he told the BBC.
"To make a bacteriophage vaccine, all you really need is a glass flask, a small amount of very cheap culture medium, and you grow the culture overnight."
Bacteriophages have evolved to live on and eat bacteria.
In the Soviet Union, they were used as medicines against bacterial diseases - a kind of live antibiotic. But the latest concept is completely different. The phages are vehicles for delivering vaccine - in theory, against a number of diseases with a single shot.
"In theory, we could probably put anywhere up to about 10 vaccines in the same bacteriophage," says Dr March. "So what it would mean is that you would have one immunisation and hopefully it would be able to protect against 10 diseases simultaneously."
The bacteriophage concept is related to the idea of DNA vaccination. Conventional vaccines use a harmless version of the organism which causes the disease you want to protect against, whether it is a virus or a bacterium; or it uses proteins which lurk on the organism's surface.
A decade or so ago, however, scientists realised there was another possible approach. Rather than injecting bits of the organism itself, why not inject bits of its DNA? Like many of the best ideas in science, the concept was discovered by accident, as Dr Martin Friede, a vaccine specialist with the WHO, explains.
"This shouldn't really work," he says. "This was originally done as part of a gene therapy experiment. People injected the DNA and discovered that it expressed protein in the body; and an immune response was made to the protein.
"So this was really unexpected. People were surprised that DNA was taken up; and that an immune response was generated against the product of the expression of the DNA."
In some experiments DNA vaccination proved a spectacular success - in mice. For some reason, which scientists are still trying to work out, it has not transferred its success to larger animals, including humans.
Researchers are still pursuing it avidly, however, because for some of the world's biggest diseases, such as malaria, the conventional approach to vaccination simply does not work.
Phage vaccination, John March has shown, does induce immunity in mice - but will it work in humans?
"I don't want to be negative because if this were to work, it would be a great thing. But there are a lot of very basic questions that need to be asked," says the WHO's Martin Friede.
Asking them requires money. So far, the work has been funded by the development agency Scottish Enterprise - but more will be needed to scale up research to larger animals.