Researchers are to expand a clinical trial of a new malaria vaccine after promising results in a preliminary study in Burkina Faso.The trial was designed to test safety, but researchers found that vaccinated children had high levels of protection.Described as a "most encouraging" result, a larger study involving 800 children is now to take place in Mali.The scientists involved say they are hopeful that the vaccine will ultimately be very cheap to produce.Around a hundred different malaria vaccine candidates have been developed to date but the MSP3 vaccine tested in Burkina Faso is only the second one to show a substantial level of protection against the illness.The randomised, double blind study involved 45 children. It set out to test the safety of the vaccine but this follow up study found that children who received it had an incidence of the disease three to four times lower than children who did not.Initially the children were split into three groups, with two of them receiving the experimental malaria vaccine developed by Dr Pierre Druilhe at the Pasteur Institute in Paris."Those two groups had very similar types of immune response, elicited by the vaccine, and the protection is almost identical, so it reinforces the confidence despite the fact that we are still dealing with a small group," he said.The vaccine is based on the fact that some adults in Africa acquire immunity because they are constantly exposed to the disease.Early daysDr Druilhe and his team discovered a key protein, MSP3, which provokes the body into producing antibodies that kill the parasite.He said the protein is unique as it does not change much between different strains of the plasmodium parasite that causes malaria. This is believed to be a critical factor in developing an efficient vaccine.He added: "We performed a large number of epidemiological studies that confirm that there was an association between that vaccine candidate and acquired protection, so when you immunise with this molecule you indeed induce protection."Another scientist involved with the Burkina Faso study was Dr Louis Miller, the former head of the Malaria Vaccine Branch of the US National Institutes of Health.He said: "I was always in favour of this approach as it offered a chance in a field with few successes. I found the results of this preliminary study in Burkina Faso to be most encouraging."High transmissionEncouraged by the early results, Dr Druilhe said the trial has now been expanded to 800 children in Mali. But he remains cautious."There have been too many claims of effective vaccines so we have to remain very cautious. It has to be confirmed and we have started on work to do that confirmation. Essentially the trial in Mali is about 20 times larger, in extremely high transmission conditions, so it should yield very clear cut results - this will be black and white."The other vaccine candidate that has shown success against malaria is called RTS, S. It has been funded by the Bill and Melinda Gates Foundation and is set to go into production with pharmaceutical giant, GlaxoSmithKline.But there are concerns that it could be expensive, especially for people in Africa and other regions affected by the disease.Dr Druilhe says his vaccine could be a lot cheaper - perhaps half a dollar or less a bottle.The results of the Burkina Faso trial were published in The New England Journal of Medicine.