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U.S. Launching Human Trial of SARS Vaccine

DNA-based vaccine has several advantages, experts say

TUESDAY, Dec. 14, 2004 (HealthDayNews) -- An experimental vaccine for SARS, the virulent and potentially fatal respiratory illness, has several advantages over traditional vaccines, a leading federal health researcher said Tuesday.

Details of the vaccine's unique design are emerging in the wake of Monday's announcement by the National Institute of Allergy and Infectious Diseases that it will begin human testing of the vaccine in the United States.

Ten healthy volunteers will undergo periodic follow-up exams for 32 weeks as part of a study primarily designed to see whether the vaccine is safe for human use. Investigators also want to assess the vaccine's ability to produce antibodies and cellular immunity against the disease.

What's different about this vaccine is that it uses a piece of DNA that produces one of the proteins normally made by the SARS vaccine. Because it is synthesized in a laboratory, it's also safer than traditional vaccines that use inactivated or weakened virus, said Dr. Gary J. Nabel, director of the NIAID's Vaccine Research Center, which spearheaded the vaccine's development.

"You couldn't possibly become infected by this vaccine," he said.

The vaccine also triggers a different kind of immune response than other vaccines, Nabel added. "The DNA vaccine actually does allow us to stimulate both the cellular arm of the immune system as well as making an antibody response," he said.

SARS, or severe acute respiratory syndrome, caught the world off-guard when it first surfaced in China in November 2002. The disease killed 774 people and sickened 8,096 by July 2003 before it was contained through aggressive public health measures, including quarantines and stringent travel restrictions.

SARS is caused by a previously unidentified coronovirus and usually begins with a fever of more than 100.4 degrees Fahrenheit. Other symptoms may include chills, headache, general discomfort and body aches.

The U.S. vaccine is the second to begin a human trial against SARS. Chinese researchers began human testing of a vaccine in May using an inactivated SARS virus.

Nine months ago, however, U.S. scientists reported positive results from an experimental SARS vaccine given to mice. The researchers fashioned the vaccine from a segment of DNA that codes for a protein found on the outer surface of the SARS virus -- called a spike protein.

To have a vaccine move to human trials just 21 months after international health officials first recognized SARS as a new infectious disease is unprecedented, federal officials said. It often takes decades to develop a successful vaccine against an infectious disease. U.S. health officials credited the use of powerful new research tools for dramatically cutting the development time.

"This experimental vaccine is an outstanding achievement by NIAID researchers," Health and Human Services Secretary Tommy G. Thompson said Monday in a statement. "It is a model for research that could greatly shorten the time needed to create vaccines to be tested against other diseases," he added.

Nabel said the swift response of the World Health Organization and the U.S. Centers for Disease Control and Prevention in identifying the SARS virus also helped. Within 10 days, the virus had been isolated; within a month, the entire DNA sequence was known, he said.

Several Asian nations, particularly China, as well as Canada were hardest hit by the first -- and last -- global SARS outbreak. There were only eight confirmed cases in the United States and no SARS-related deaths in 2003, the CDC said.

Striving to prevent another global outbreak, WHO continues to lead an international effort to detect cases of the disease at their onset. In revised surveillance and reporting guidelines issued in October, the agency said the most probable source of infection, at the moment, is in laboratories where the virus is used or stored.

Nevertheless, the agency warned countries against becoming complacent: "It remains very difficult to predict when or whether SARS will re-emerge in epidemic form," a WHO statement said.

Vical Inc., a San Diego-based vaccine developer, is under contract with NIAID to produce the vaccine for the U.S. clinical trial. Even if all goes well, Nabel cautioned, it could take another three to five years to wrap up testing and get a vaccine approved for widespread use.

Likely candidates for such a vaccine would include health-care workers in areas where the disease might break out again and workers in laboratories handling the virus, he said.

Should another outbreak occur before a human vaccine is approved for use in the United States, Americans can protect themselves by taking the same sort of common-sense precautions recommended for avoiding all sorts of infectious disease.

The most important step is frequent handwashing with soap and water or use of an alcohol-based hand rub, the CDC advised. People also should avoid touching their eyes, nose and mouth with unclean hands, and they should encourage those around them who are coughing or sneezing to cover their mouth and nose with a tissue.

More information

For more on SARS, visit the U.S. Centers for Disease Control and Prevention.

SOURCES: Gary J. Nabel, M.D., director, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Md.; Dec. 13, 2004, NIAID press release; April 1, 2004, Nature; U.S. Centers for Disease Control and Prevention, Atlanta; October 2004, World Health Organization guidelines for the global surveillance of SARS
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