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Administration of the shingles vaccine in patients with active acute ocular zoster infection is not indicated, and use of the vaccine in a patient with active interstitial keratitis actually may worsen the disease.
San Francisco-Administration of the shingles vaccine in patients with active acute ocular zoster infection is not indicated, and use of the vaccine in a patient with active interstitial keratitis actually may worsen the disease.
Dr. Margolis discussed considerations surrounding this relatively new treatment. Once an individual is infected with the varicella zoster virus during childhood, the virus remains latent in the sensory neurons, and the chicken pox virus can be reactivated later in life as a shingles infection. When the eye is affected, it is referred to as herpes zoster ophthalmicus.
Mechanism of immunity
Dr. Margolis explained the mechanism of immunity after exposure to the zoster virus over the course of years.
"The thought is that subclinical reactivation of the virus is why the immunity lasts over time," Dr. Margolis said. "With periodic exposure to children with the virus, immunity is boosted throughout life, and shingles does not develop. Over time and with aging of the immune system-and without that continued exposure to children with chicken pox who are shedding virus-the immunity level drops below a certain threshold and herpes zoster develops.
"The reason people do not [have] recurrences of the virus is that [they] literally are vaccinated by their own virus, although with time the immunity can wane and a second episode can occur," he said. "There also can be subclinical reactivations that again boost the immunity."
The varicella vaccine that has been administered to children since 1995 has led to a marked decrease in varicella cases. However, there have been breakthrough cases in patients immunized early. In 2006, the two-dose immunization schedule was instituted. Time will tell if that solves the problem of breakthrough cases, he said.
A study in 2009 of shingles looked at a cohort of children in Antelope Valley, CA. The thesis of the study was that if children are vaccinated, the shedding of the varicella virus is eliminated, and unvaccinated children may develop shingles because of their lack of immunity. The study found an increased incidence of shingles in unvaccinated children aged 10 to 19 years.
"This result fits with the idea that being exposed to other kids who are shedding the virus increases immunity and prevents the development of shingles," Dr. Margolis said.
The zoster vaccine for adults basically is the same as that for children, except the adult vaccination contains about thirteen-fold more virus. The vaccine was approved by the FDA in 2006 for patients who are aged 60 or more years. Efficacy studies of the vaccine indicate that it decreases the incidence of zoster by 50%. Patients who develop zoster despite being immunized experience reduced severity and duration of the zoster episodes and, more importantly, the incidence of postherpetic neuralgia.
There still is a question about who should receive the vaccine, however.
"Administering the vaccine to patients under the age of 60 years may turn out to be a good idea because young age facilitates a better response to the vaccine than older age," Dr. Margolis said. "Patients in their 70s do not get nearly as good an immune response as those in their 60s. However, the efficacy and safety of the vaccine has only been studied in patients who are 60 years and older."
Children, pregnant women, and immunocompromised individuals should not receive this vaccine because it contains live-attenuated virus. In addition, in immunocompromised individuals, there will be a decreased immune response, making the benefit of the vaccine questionable. In this situation, there is potential to develop zoster. Also unknown is the duration of the protection from the vaccine. Currently, there are no recommendations to revaccinate.