Examination of links between herpes zoster incidence and childhood varicella vaccination

Abstract

Background: Introduction of a universal varicella vaccine program for U.S. children in 1996 sparked concern that less-frequent exposure to varicella would decrease external boosting of immunity to varicella zoster virus and thereby increase incidence of herpes zoster (HZ).

Objective: To determine whether the varicella vaccination program has influenced trends in HZ incidence in the U.S. population older than 65 years.

Design: Retrospective study of Medicare claims.

Setting: Medicare, 1992 through 2010.

Participants: 2 848 765 beneficiaries older than 65 years.

Measurements: Annual HZ incidence from 1992 through 2010; rate ratios (RRs) for HZ incidence by age, sex, and race or ethnicity; and state-level varicella vaccination coverage.

Results: 281 317 incident cases of HZ occurred. Age- and sex-standardized HZ incidence increased 39% from 10.0 per 1000 person-years in 1992 to 13.9 per 1000 person-years in 2010 with no evidence of a statistically significant change in the rate of increase after introduction of the varicella vaccination program. Before introduction of this program, HZ incidence was higher in women (RR, 1.21 [95% CI, 1.19 to 1.24]) than men and was lower in black persons (RR, 0.51 [CI, 0.48 to 0.53]) and Hispanic persons (RR, 0.76 [CI, 0.72 to 0.81]) than white persons. In a model adjusted for sex, age, and calendar year from 1997 to 2010, HZ incidence did not vary by state varicella vaccination coverage (RR, 0.9998 [CI, 0.9993 to 1.0003]).

Limitation: Uncertain level and consistency of health-seeking behavior and access and uncertain accuracy of disease coding.

Conclusion: Age-specific HZ incidence increased in the U.S. population older than 65 years even before implementation of the childhood varicella vaccination program. Introduction and widespread use of the vaccine did not seem to affect this increase. This information is reassuring for countries considering universal varicella vaccination.

Primary funding source: None.

Figure 1. HZ incidence among Medicare beneficiaries older than 65 years, by age group, 1992–2010

HZ = herpes zoster.

Appendix Figure 1. Age- and sex-standardized HZ incidence among immunocompetent Medicare beneficiaries older than 65 years, 1992–2010

This immunocompetent subpopulation excluded beneficiaries with any International Classification of Diseases, Ninth Revision, Clinical Modification, code indicating a potentially immunocompromising condition or a condition that may be managed with immunosuppressive treatment (see Appendix Table for the list of codes). HZ = herpes zoster.

Appendix Figure 2. Age- and sex-standardized ratios of HZ incidence to the incidence of 10 selected conditions, 1995–2010

The 10 conditions and associated International Classification of Diseases, Ninth Revision, Clinical Modification, codes were impacted cerumen (380.4), calculus of kidney and ureter (592.x), urinary tract infection (599.0), ingrowing nail (703.0), lipoma (214.x), sprains and strains of wrist and hand (842.xx), inflammation of eyelids (373.xx), epistaxis (784.7), hemorrhoids (455.x), and gout (274.0, 274.9). HZ = herpes zoster.