As varicella recedes, zoster rises: the question is 'why?'.
WASHINGTON -- As the number of children vaccinated against varicella has risen, the number of chicken pox cases has proportionally declined.
No news there.
But, as the number of children getting chicken pox gets smaller, the number of adults getting shingles is growing--and no one really knows why, Dr. Vikash Oza said at the annual meeting of the American Academy of Dermatology.
"Varicella vaccination has had a dramatic impact on the incidence of chicken pox," said Dr. Oza, a pediatric dermatologist at New York University Langone Medical Center. "In fact, as a resident I saw not one case of chicken pox. That's pretty astounding considering how common it used to be."
Introduced in 1995, the vaccine now covers about 90% of children in this country--an achievement almost exactly mirrored by the decrease in disease incidence. In fact, according to a 2013 study, the bang for the vaccine buck may be even bigger, achieving 98% decreases in two regions examined (Pediatrics. 2013; 132:el 134-40).
That study also found that vaccinated children who did get chicken pox had much milder infections that resolved more quickly.
Again, that's good news, but not particularly surprising, said Dr. Oza. The more intriguing change is the steady increase in herpes zoster among older adults occurring in tandem with the decreased incidence of chicken pox. Cases were up a total of 39% from 1992 to 2010 among adults 65 and older, according to the Centers for Disease Control and Prevention (Ann Intern Med. 2013; 159:739-45).
"This thing that's happening in adults is quite interesting," Dr. Oza said. "Although zoster in children is uncommon, we do know that children are much less likely to develop it if they've been vaccinated against varicella. What we don't really know is what this means for adults. One of the effects of the vaccine, of course, is less circulating varicella zoster virus in our communities. It's possible that a benefit of having some circulating VZV gives adults an immune boost that keeps zoster in check, and without that, developing shingles is more likely."
Several recent studies have documented the association. A 2005 study found that during 1998-2003 the incidence of chicken pox in Massachusetts went down by 79%, while the incidence of shingles increased by 90% (BMC Public Health 2005; 5:68). But a shifting age-related immune response is only one possible explanation, the authors wrote. "Other possible explanations include increases in the proportion of people with immunosuppressive conditions and therapies, in the duration of those conditions and treatments, and/or in the prevalence of other triggering factors."
The shifting incidences of chicken pox and shingles, however, were predicted years before they occurred. A mathematical model from 1992 predicted a long-term elevation of up to 20% in the shingles rate, relative to the prevaccination incidence (Epidemiol Infect. 1992; 108:513-28).
A 2001 paper predicted that shingles would increase for 30-50 years after mass varicella vaccination, rising to a maximum of about 50% above prevaccination rates, before falling below baseline levels (Epidemiol Infect. 2001; 127:305-14).
The CDC refutes any causative link between varicella vaccinations and shingles. "This proposed explanation seems unlikely based on two CDC studies which found that shingles rates started increasing before chicken pox vaccine was introduced in the United States, and after the routine chicken pox vaccination program started," the agency's surveillance page notes.
Regardless of the "why" behind the association, Dr. Oza said he expects it to level out as vaccinated children come of shingles age.
He had no financial disclosures.
Please note: Illustration(s) are not available due to copyright restrictions.
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|Title Annotation:||MEDICAL DERMATOLOGY|
|Author:||Sullivan, Michele G.|
|Date:||May 1, 2016|
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