Prevention, Almost PerfectBefore the FDA approved the chickenpox vaccine in 1995, about 95 percent of the U.S. population developed chickenpox before age 18. Since then, more than 60 percent of American youngsters have been vaccinated against chickenpox.
"The vaccine is a live attenuated strain of the chickenpox virus," says Philip R. Krause, M.D., lead research investigator in the FDA's Center for Biologics Evaluation and Research. "However, it's a weaker form so it gives rise to a milder infection. But in the course of giving rise to this milder infection, it induces enough immunity to prevent people from getting the natural infection." It is estimated that the vaccine is between 75 and 85 percent effective in preventing chickenpox. "But the important thing," says Krause, "is that it is almost completely effective in preventing severe cases of chickenpox."
Now that we have a chickenpox vaccine, are shingles and PHN on their way out? Although the FDA hasn't evaluated the effects of the vaccine on shingles, Krause believes that "in the long term, if you can prevent enough people from getting the wild (natural) type of chickenpox, you're likely to see a beneficial effect on the incidence of shingles and post-herpetic neuralgia. But it may take several generations for this to happen."
People who have had chickenpox (varicella zoster) in their youth can develop shingles (herpes zoster) in later years. During an acute attack of the chickenpox virus, most of the viral organisms are destroyed, but some survive, travel up nerve fibers along the spine, and lodge in nerve cells where they may lie dormant for many years. A decrease in the body's resistance can cause the virus to reawaken decades later. It then travels back down the nerve fibers to the skin's surface.
The reawakened virus generally causes a vague burning sensation or tingling over an area of skin. A painful rash usually occurs two to five days after the first symptoms appear. A cluster of small bumps (1) turns into blisters (2) that resemble chickenpox lesions. The blisters fill with pus, break open (3), crust over (4), and finally disappear. This process takes four to five weeks.
A painful condition called post-herpetic neuralgia can sometimes occur. This condition is thought to be caused by damage to the nerves (5), and can last from weeks to years after the rash disappears.
Shingles Prevention Study
Since shingles can be very serious in older people, the Department of Veterans Affairs, the National Institute of Allergy and Infectious Diseases, and Merck & Co. Inc. are conducting a five-year clinical study at 22 sites nationwide to determine whether vaccination can prevent shingles in people ages 60 years and older who have had chickenpox.
As with the chickenpox vaccine now in use, the experimental vaccine is made from a weakened form of the chickenpox virus, but is much more potent than the existing vaccine.
"Immunity to the virus declines with advancing age, making older adults vulnerable to shingles," says Norberto Soto, M.D., principal investigator for the Shingles Prevention Study at the National Institutes of Health site in Bethesda, Md. "We believe that by boosting the body's immune response with this vaccine, shingles and its complications may be prevented."
The clinical trial hopes to recruit 37,200 volunteers. Besides the age requirement, the enrollees must be in good health and never have experienced shingles.
The study, which began in 1999, is a "double-blind" study, which means that neither the researchers nor the participants know who is receiving the experimental vaccine or an inactive substance (placebo).
If the vaccine is effective, it may help reduce illness and health-care costs among older people.
FDA Consumer magazine
By Evelyn Zamula