A new kind of malaria vaccine that mimics the effects of mosquito bites has shown early promise by offering 100 per cent protection to a dozen human volunteers, researchers said.
The experimental vaccine, called PfSPZ and produced by the US-based company Sanaria, contains live malaria parasites collected through a painstaking process of dissecting the salivary glands of mosquitoes.
These immature parasites, known as sporozoites, are then weakened so they cannot cause illness and are incorporated into a vaccine, which must be injected into a person's veins several times, with each shot about a month apart.
"When we started doing this, everybody knew that sporozoites were the gold standard but everyone thought it was impossible to make a vaccine out of sporozoites and we were crazy. And we have proven them wrong," Stephen Hoffman, chief scientific officer of Sanaria, based in the state of Maryland, said on Thursday.
A test of the same vaccine two years ago that administered it into the skin of patients, the way most vaccines are given, showed protection in only two of 44 volunteers.
But the latest trial showed that injecting the vaccine into the bloodstream protected against malaria in all six volunteers who received a five-shot regimen at the highest dosage, according to the results published in the US journal Science.
Six of nine volunteers in a separate group that received four shots of the highest dose - 135,000 sporozoites per injection - were also fully protected against malaria, it said.
The phase I study involved 57 people - 40 who received the vaccine in varying doses and 17 controls.
"We are encouraged by this important step forward," said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.
The study was co-authored by Hoffman and Robert Seder of the institute.
There is no vaccine on the market for malaria, which infected some 220 million people in 2010 and killed 660,000 according to the World Health Organisation. Most of the deaths were among children in Africa.
Another vaccine effort under way is the RTS,S trial. Its phase III results showed 31 per cent effectiveness in young infants and 56 per cent in older babies and toddlers.
Hoffman told Science he realised years ago that a single protein vaccine like RTS,S would "never do the job" of warding off malaria, which is caused by a 5,000-gene parasite.
He was inspired instead by studies in the 1970s that showed 90 per cent of volunteers were protected against malaria after getting more than 1,000 bites from infected mosquitoes that had undergone radiation to weaken the Plasmodium falciparum parasite.
Hoffman said his product is believed to protect against malaria for a period of six to 10 months. Several small clinical trials are planned next for Tanzania, Germany and the United States.
Hoffman estimated it would be four years before a vaccine may reach the marketplace. He said about US$110 million had been invested so far.