New SARS Vaccine Works in Mice, Human Trials Near

A new, experimental vaccine against SARS that protects mice from the infectious disease could soon be tested in humans, scientists said on Wednesday.

A new, experimental vaccine against SARS that protects mice from the infectious disease could soon be tested in humans, scientists said on Wednesday. The vaccine, which contains a small piece of DNA from the virus that causes the respiratory illness, stopped it replicating in infected mice. “The good news from this study is that it really provides the first proof of concept that you can vaccinate and you can get immune protection against the SARS coronavirus,” said Dr Gary Nabel of the National Institute of Allergy and Infectious Diseases (NIAID) in the United States. “It also provides the first description of an immune mechanism by which that occurs,” he added in an interview. “That is important for developing a human vaccine and for developing antiviral therapies.” Severe Acute Respiratory Syndrome (SARS) first emerged in southern China in 2002. It infected more than 8,000 people in nearly 30 countries and killed nearly 800. Although the outbreak was brought under control, public health experts say it could re-emerge. Scientists identified its cause as a new virus from the family of so-called coronaviruses that are responsible for the common cold and a range of animal illnesses. China, Hong Kong and Canada were among the most severely affected by the virus which spread around the world through international air travel. The vaccine developed by Nabel and his team is made from a tiny piece of modified SARS DNA linked to a protein on the outer surface of the virus. The protein helps the virus infect cells. The DNA used in the vaccine is too small to reproduce the SARS virus but sufficient to stimulate an immune response. The scientists tested two versions of the vaccine containing different amounts of genetic material from the virus and compared the results with mice that were not vaccinated. Mice injected with the vaccine launched an immune response against the virus shortly after they were infected. Animals that had been vaccinated had one million times fewer virus particles in their lungs than the non-vaccinated mice, according to the research published in the science journal Nature.Nabel and his colleagues hope to begin small human trials of the vaccine by the end of the year. “But we need to proceed cautiously because as we know with some other coronaviruses there are some instances where vaccines can actually make the problem worse,” he said. Although the vaccine was effective in mice, Nabel said the animal models may not reflect the severity of the illness in humans. He and his team are working with California biotechnology company Vical Inc to manufacture a purified vaccine in preparation for human trials. China has already received approval for human trials of another SARS vaccine. Other teams of researchers are also working on different types of vaccines for the virus. Using a combination of vaccines is also a possibility and could prove more effective than a single product, according to Nabel. DNA vaccines have a good safety profile in humans but more research is needed to test their efficacy in humans, he said. “I think it is only a matter of time before we will have the opportunity to do that,” Nabel added.(Source: Reuters Health, March 2004)