Zoster Vaccine Well Tolerated in Adults

Emma Hitt, PhD

April 23, 2012

April 23, 2012 — The risk for severe adverse events up to 42 days after zoster vaccination of adults aged 50 years or older was no more than expected on the basis of risk in a comparison period, according to the findings of a large managed care cohort study. However, the risk for allergic reaction was increased by 10-fold in the 50- to 59-year-old age group, report Hung Fu Tseng, PhD, MPH, from Southern California Kaiser Permanente, Pasadena, and colleagues.

The team evaluated the safety profile of zoster vaccine among 193,083 adults aged 50 years or older in 8 managed care organizations. The researchers published the findings online April 23 in the Journal of Internal Medicine.

"Post-marketing safety information on the vaccine is limited," the authors write. Such studies provide information on the safety of the vaccine in clinical practices with physiologically heterogeneous populations.

The Vaccine Safety Datalink (VSD) project, funded by the Centers for Disease Control and Prevention, was designed to detect rare and serious adverse events after vaccination with several commonly recommended vaccines.

The investigators used computerized data to identify any adult who died or who experienced 1 of several other prespecified events. Five major groups of events of interest were stroke and cerebrovascular diseases; cardiovascular diseases; meningitis, encephalitis, and encephalopathy; Ramsay-Hunt syndrome and Bell's palsy; and reactions leading to a medical visit.

The researchers used 2 within-person comparison methods, the case-centered and the self-controlled case series (SCCS) methods, to estimated the effect of the vaccine. According to the authors, these methods avoid differences between vaccinated and unvaccinated persons that are difficult to measure and control.

The case-centered design is anchored by the date of the adverse event. In theory, this method compares the "observed" and "expected" probability of receiving the vaccine within the prespecified risk window. By contrast, the SCCS method is anchored by the vaccination date and looks forward to identify the adverse event of interest after vaccination.

The only significantly increased risk the researchers identified was allergic reactions in the outpatient and emergency department setting in the 1- to 7-day window after vaccination (relative risk [RR] by case-centered method, 2.13; 95% confidence interval [CI], 1.87 - 2.40; RR by SCCS, 2.32; 95% CI, 1.85 - 2.91). Medical record abstraction of these cases revealed that more than 80% of these events involved a localized inflammatory response, including redness, swelling, or tenderness at the injection site.

Allergic reactions were particularly common among persons aged 50 to 59 years (10-fold increased risk; RR by case-centered method, 11.07; 95% CI, 6.68 - 18.33; RR by SCCS, 10.00; 95% CI, 2.34 - 42.78). The risk was also increased more than 2.5-fold and 1.5-fold among patients aged 60 to 69 years and 70 to 79 years, respectively; no increase in risk was seen among patients aged 80 years or older.

According to the authors, these findings are consistent with previous studies, which led those researchers to suggest that the adverse events may be mediated by immune responses to the attenuated vaccine virus. This response may be more vigorous in younger patients.

Furthermore, Dr. Tseng and colleagues report that a small increased risk for cellulitis identified in the VSD project within the first week after vaccination (RR, 1.30; 95% CI, 1.18 - 1.44) may represent inflammatory or allergic reactions rather than true cellulitis.

"The results of this study support the findings from the prelicensure clinical trials, providing reassurance that the zoster vaccine is generally safe and well-tolerated with a low increased risk of inflammatory or allergic reactions," the authors state. "The causes of an elevated risk of these reactions among the 50-59 year age group warrant further investigation."

This study was funded through a subcontract with America’s Health Insurance Plans under contract 200-2002-00732 from the Centers for Disease Control and Prevention. The researchers have disclosed no relevant financial relationships.

J Intern Med. Published online April 23, 2012.

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