Researchers in america have published the promising results of trials of an experimental malaria vaccine produced by Sanaria Inc. The trials， conducted by the United States National Institutes of Health， working alongside the U.S. Navy and Army between October 2011 and October 2012， involved giving 40 healthy， adult volunteers intravenous doses of the vaccine. Six of the volunteers were given five large doses of vaccine， and none were infected after being bitten by mosquitoes carrying the same strain of malaria from which the vaccine had been made. Unfortunately， administering smaller or fewer doses of the vaccine did not yield the same results. Three of the nine volunteers who received only four doses of vaccine were infected with malaria after being bitten， and infection rates were even higher for other trial groups that were given smaller or fewer doses of vaccine， with 11 members of the 12-person control group （which received no vaccine） being infected after being bitten by mosquitoes carrying the disease.
　　While the scientific community is celebrating this as a major advance in the fight against malaria， they caution that the expense and resources involved in producing and administering the vaccine make it impractical to use on a large scale at this time. For the vaccine to be 100-percent effective， recipients must receive five intravenous doses of the vaccine. Administering the vaccine in this way requires sterile conditions to lessen the risk of infection， and the work of highly skilled healthcare professionals.
　　Producing the vaccine in the quantities required to immunize at-risk populations would also be prohibitively expensive. To create the vaccine， Sanaria’s team of scientists bred mosquitoes in sterile conditions， and then fed them blood that was infected with malaria. The mosquitoes were soon carrying malaria sporozoites， which Hoffman then weakened by exposing the mosquitoes to radiation. Extracting the weakened sporozoites from the infected mosquitoes required trained technicians to perform hundreds of micro-surgeries to remove the salivary glands of the infected mosquitoes. The sporozoites were then frozen and processed to produce the vaccine.
　　As malaria is a parasite， it cycles through different developmental phases after it infects a host. This has made the creation of a vaccine for malaria more complicated than the development of vaccines against viral or bacterial infections， as scientists had to decide which malaria parasite is introduced to the body form of the sporozoite. By creating a vaccine that immunizes people against this phase of the disease， scientists have ensured that recipients of the vaccine will have an immune response that will fight and eradicate the parasite before it has a chance to move to the next stage of its development.
　　While this initial trial showed the vaccine to be safe and effective if administered in larger doses， larger vaccine trials are scheduled to take place later this year in Tanzania and Mali. These trials will focus on testing how long and to what extent the vaccine protects against malaria infection in regions where trial participants are at risk of contracting the disease.
　　Due to the expense of producing the vaccine， it will likely only be available to very limited groups until its production costs can be lowered substantially. At the moment， experts see military personnel and wealthy tourists planning on spending time in regions where they would be at risk of contracting malaria as the primary beneficiaries of this scientific advance.