A new type of vaccine that is cheaper and easier to produce than traditional vaccines may some day be used to protect people from diseases such as malaria, researchers say. The new type of vaccine uses a virus's DNA to build up the body's immunity. Scientists tested it on humans for the first time in a study published in the journal Science. The researchers injected 20 human volunteers with a DNA vaccine for malaria. After six weeks, their blood showed a buildup of cytotoxic T lymphocytes, killer cells that fight infections.