SAN FRANCISCO--There is a critical need for a new, effective vaccine to fight tuberculosis, which causes more adult deaths worldwide than any other infectious disease, a TB specialist at the University of California San Francisco emphasized here today.
Speaking at the International Symposium on TB Vaccine Development and Evaluation, Philip C. Hopewell, MD, professor of medicine and associate dean for the UCSF School of Medicine at San Francisco General Hospital, outlined the clinical characteristics of the ideal vaccine.
Most important, he said, is a new model that offers protection at three levels: prevents new infection, prevents persons already infected with TB from developing active TB disease, and prevents reinfection in those who previously had been infected. "This would halt the chain that perpetuates widespread infection, and it is the only way to effectively eliminate TB as a global health problem," he added.
At present, the only existing TB vaccine is the bacille Calmette-Guerin (BCG) vaccine, which has prevented deaths in children but has not proved protective in adults. BCG has been in use for the past 70 years primarily in developing countries, but it has had little impact on the spread of TB, he said.
Recognized nationally in the field of TB control and prevention, Hopewell said the worldwide goal of disease elimination in the next few years is finally realistic because the U.S. public health community is now coming together for the first time with total support for new TB vaccine development.
"This meeting is part of the commitment and it includes all the right experts--from national and international groups--to make it happen," he said. "In addition, scientific advances in understanding the genetic and molecular structure of the TB bacteria make creation of the ideal vaccine more doable." "A basic premise of a new vaccine is that it should be feasible in all areas of the world," Hopewell said.
Other ideal characteristics are:
- Ease of administration.
- Safe even in persons who are immunocompromised--The current vaccine is comprised of a live, attenuated form of an organism that is closely related to the organism that causes TB. There is the potential for it to cause TB in persons with weakened immune systems, such as HIV/AIDS patients.
- Does not cause a positive skin test reaction (tuberculin skin test)--BCG causes the tuberculin skin test, which is used to identify new infections, to produce a false-positive result, thereby complicating the TB screening process.
- Stable composition -- Not heat, cold or light sensitive so that storage is easy.
Caused by the organism Mycobacterium tuberculosis, TB is a chronic bacterial infection that usually affects the lungs but also attacks other organs. It is spread through the air when a person with active TB disease of the lungs or larynx coughs, sneezes, or shouts. It is most prevalent in densely populated areas and the inner-city where people often live in close quarters.
Worldwide, an estimated 2 billion persons--one-third of the world population--are infected with TB, and about 3 million die each year from the disease. Areas with the highest rates of infection include Sub-Saharan Africa, India, China, and the Philippines.
An estimated 15 million Americans are infected, although only about 10 percent of those infected ever develop the disease. An estimated 10-12 percent of the San Francisco population is infected.
Factors contributing to TB infection rates in the U.S. include the HIV/AIDS epidemic, because persons with HIV are particularly vulnerable to infection; increased numbers of immigrants from countries with a high incidence of TB and crowded housing; and an increased population of homeless and injection drug users.
Over the past decade, spread of the disease in the U.S. has been effectively controlled through public health programs that focus on early diagnosis and treatment and on follow-up with contacts of infectious patients. Still, the rate of TB in the U.S. is nearly 75 times higher than the level necessary to completely eliminate the disease nationally, according to Hopewell With early diagnosis, TB can be successfully treated with a 6-month regimen of medication, but strict compliance is necessary or drug-resistance can develop.
"While our public health strategy may be considered an effective control measure, it also is inefficient because it relies on the identification of symptomatic patients who may already have spread infection," Hopewell said.
In developing nations, screening programs and treatment follow-up are difficult to maintain because of limited resources, which underscores the critical need for a vaccine, he added.
The three-day symposium in San Francisco is co-sponsored by the National Institute of Allergy and Infectious Disease, American Lung Association of Metropolitan Chicago, International Union Against Tuberculosis and Lung Disease, Centers for Disease Control and Prevention, and World Health Organization.
Note To The Media:
Reporters who would like to interview Dr. Hopewell can reach him through his UCSF/SFGH office at (415) 206-8509.
The International Symposium on TB Vaccine Development and Evaluation is taking place August 26-28 at the Parc Fifty-Five Hotel in San Francisco (415) 392-8000.