Researchers at the US National Institute of Allergy and Infectious Diseases (NIAID) have launched a trial to test the safety of a preventive vaccine against severe acute respiratory syndrome (SARS). The DNA vaccine, which encodes the spike glycoprotein of the SARS coronavirus, induces both a neutralising antibody response and “very good T-cell immunity”, says Gary Nabel, director of the NIAID Vaccine Research Center in Bethesda, MD. Ten healthy volunteers will receive the vaccine, and researchers will do periodic follow-up examinations over 6 months.The vaccine's mechanism of action is different from that of the inactivated virus vaccine that is being tested in China, Nabel told TLID. “That vaccine really only induces antibody responses. We think it's wise to have additional mechanisms of protection available, should the virus break through the neutralising antibody response.” The two approaches could also be complementary, he notes. “One of the things we are now testing in animals is the ability of the DNA to prime an immune response generating both the cellular and humoral response, then boosting it with inactivated virus. This gives us another way to modulate immune function.”NIAID pushed ahead with the vaccine after Gabel and colleagues showed that it reduced viral replication by more than six orders of magnitude in the lungs of infectedmice (Nature 2004; 428: 561–64). Moreover, “the technology could be developed quickly, because we've been using it for AIDS and Ebola vaccine, so we had everything in place to move forward rapidly”, says Gabel. And, he adds, “it's a safer vaccine to make and administer compared with the inactivated virus vaccine, because the workers who grow the wild-type viruses are exposed. They've done it safely so far, but the more we can avoid working with the virus, particularly in large supply, the better off we'll be from a public health perspective”.