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Herpes zoster incidence unaffected by varicella vaccine programs
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Researchers from the CDC’s National Center for Immunization and Respiratory Diseases have found that the widespread use of childhood varicella vaccinations did not affect the increase of herpes zoster usually seen among adults older than 65 years.
“In the absence of explanations for increasing herpes zoster incidence, properly monitoring the effect of the herpes zoster vaccination program or projecting future herpes zoster incidence will be difficult,” the researchers wrote in the Annals of Internal Medicine.
Using health care claims data on a 5% random sample of Medicare beneficiaries, the researchers analyzed the incidence of herpes zoster from 1992 to 2010. They evaluated trends during three periods of varicella vaccination program implementation: pre-implementation (1992-1995), early implementation (1996-1999) and full implementation (2000-2010). They then used state varicella vaccination data to measure the effect of implementing a varicella vaccination program on herpes zoster incidence.
The study included 2,845,353 Medicare beneficiaries and a total of 22,508,343 person-years. There were 281,317 incident cases of herpes zoster during the entire period. Age- and sex-standardize herpes zoster incidence in 1992 was 10.2 per 1,000 person-years, and in 2010, the incidence was 14.3 per 1,000 person-years, an increase of 39%. There was no change in the rate of increase after the introduction of the varicella vaccination program.
“Herpes zoster poses a substantial burden of disease in the elderly population, and continued increases in herpes zoster incidence would be worrisome and need to be understood,” the researchers wrote. “Fortunately, an effective vaccine is now available that can help prevent this disabling disease.”
Disclosure: The researchers report no relevant financial disclosures.
Perspective
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Anne Gershon, MD
Fear developed that widespread varicella vaccination would lead to an increase in herpes zoster from decreased exposure to circulating virus. Hales and colleagues therefore analyzed Medicare records from 1992-2010 to determine the incidence of herpes zoster in older individuals. Although retrospective studies have downsides, they found an increase in age-specific herpes zoster in Americans years began before licensure of varicella vaccine. Therefore, one cannot blame varicella vaccine alone for increasing in herpes zoster. Other factors such as longer lifespans, immunocompromised patients, stress, ascertainment, diabetes and statins must contribute. Just because exposure to varicella patients prevents herpes zoster does not mean this is required. Hope Simpson said in 1964, “One internal source of postponement (of herpes zoster) may be seen in the fifty or so ganglionic foci of latent infection” where silent reactivation may occur. Endogenous exposure may also be important in prevention of herpes zoster. Since vaccinees have decreased herpes zoster, eventually its incidence in the United States will decrease.
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