Officially, the cause of this increase is unknown. Yet studies suggest that at least part of the explanation could be the chickenpox vaccine.
Chickenpox and shingles are caused by the same virus, which is known as varicella zoster. Shingles cannot occur in someone who has not been previously been infected with the virus, presumably resulting in a chickenpox infection. Why, then, would the vaccine against this virus be causing more severe outbreaks later in life?
Unintended immune consequencesOnce infected with the varicella zoster virus, the body can never get rid of it. Instead, the virus hides from the immune system along a nerve root in the central nervous system. Shingles (also known as herpes zoster) occurs when some trigger (typically stress or reduced immune function) causes the virus to erupt out of the nerve root and travel to the skin. This leads to a painful rash that tends to last about a month. Although most people suffer only a single case of shingles in their lifetime, the disease can recur.
In addition to PHN, possible complications of shingles include bacterial skin infection, motor neuropathy, bladder impairment, meningitis, hearing loss, Hutchinson's sign and Ramsay Hunt Syndrome.
Alarmingly, shingles is now also starting to appear in children, which was virtually unheard of 20 years ago.
Researchers have suggested a simple explanation for why shingles rates might be on the increase, and at least some studies have supported this hypothesis: prior to the adoption of the chickenpox vaccine, nearly all children came down with chickenpox and thereby re-exposed the adults in their lives to the virus. This functioned as a "booster" to the immune system, thereby helping prevent reactivation of the virus in the form of shingles. Once vaccination became widespread, however, chickenpox rates fell and parents stopped getting the booster. When those parents started to hit the age of risk for shingles (50 and up), the rates of that disease started to climb accordingly.
Vaccine maker profits twice!Is this merely a question of trading a childhood illness for an illness of old age? Not quite, because like any drug, both the chickenpox and shingles vaccines carry their own risks. Between March 1995 and July 1998, adverse events were reported for more than one in every 1,500 cases of chickenpox vaccination. About 4 percent of these were severe, including shock, brain inflammation (encephalitis), thrombocytopenia (a blood disorder) and death.
While some vaccine supporters claim that chickenpox vaccination will eventually solve the shingles problem because people who are vaccinated do not get the initial infection required to later develop shingles, it actually remains unclear if the live virus vaccine is sufficient to cause varicella zoster to colonize the nerve root. The vaccine is simply too new to answer that question.
To make matters worse, it is unclear how much benefit the chickenpox vaccine even provides. Chickenpox was simply never a dangerous disease, having a fatality rate of only 0.00135 percent. That is, the disease infected about 3.7 million children per year and killed about 50, most of them immunocompromised.
Finally, the effectiveness of the shot at preventing varicella zoster infection is only about 70 percent. Thus, chickenpox is essentially guaranteed to remain endemic in the population and so will shingles.
In the meantime, of course, Merck — the company that makes the chickenpox vaccine and created the problem to begin with — has its own convenient solution: The company also offers a vaccine for shingles.
Sources for this article include: