Affecting an estimated one million Americans each year, herpes zoster (shingles) is caused by the same virus that causes chickenpox: the varicella-zoster virus. After an initial infection with chickenpox (varicella), the virus lies dormant in the dorsal root or cranial sensory ganglia; however, the virus can reactivate later in life, causing shingles. Shingles is estimated to affect one in every five persons during their lifetime. The frequency and severity of the infectious disease increase with advancing age.
Initial symptoms typically involve unusual or painful sensations on one side of the body or face, followed by a blistering rash. The rash is the most distinctive feature, but most debilitating is the associated pain. Approximately half of affected individuals suffer from prolonged pain (postherpetic neuralgia) for months, even years, after the rash resolves, and treatment of nerve pain is notoriously difficult. Postherpetic neuralgia has been described as burning, throbbing, stabbing, or shooting pain that may be accompanied by allodynia (pain from an otherwise innocuous stimulus such as a light breeze or the touch of soft clothing).
The efficacy of Zostavax has been evaluated in the Shingles Prevention Study. More than 38,000 patients (60 years of age or older) were randomized to receive one dose subcutaneously of either the vaccine or placebo. Participants were followed for a median duration of 3.1 years. Overall, the vaccine reduced the risk of developing shingles by 51% (315 cases versus 642 cases) and was most efficacious for those aged 60-69 years. Furthermore, the vaccination also appeared to reduce the incidence of long-term nerve pain in vaccinated individuals who went on to develop shingles, especially those over 70 years of age.
According to Monica Skomo, Pharm.D., assistant professor of pharmacy practice at Duquesne University, "There are clinically significant advantages to the vaccine in terms of the incidence of getting shingles and in the severity and duration of postherpetic neuralgia." The most common adverse events reported after immunization with Zostavax were injection site reactions: erythema (33.7%), pain and ten-derness (33.4%), and swelling (24.9%). Less common adverse effects included hematoma, pruritus, headache, and warmth.
As with all live vaccines, there is a theoretical risk of transmitting the vaccine virus to varicella-susceptible individuals, including pregnant women and children who have not had chickenpox or been vaccinated, as well as close immunocompromised contacts.
The overall efficacy of Zostavax in preventing herpes zoster is about 50% in clinical studies. Even with the vaccine, a substantial number of individuals may still be affected by shingles and its accompanying pain.
Skomo sees the Zostavax approval as an educational opportunity. "Even if your state doesn't allow pharmacists to immunize or if you are not an immunizing R.Ph., you can tell patients that there is an alternative-there is a vaccine. You can tell them of its importance, what to expect from it, and its benefits."
THE AUTHOR is a medical writer based in Pennsylvania.
TIPS TO REMEMBER........ Zostavax