CDC Analyzes Link Between Chickenpox Vaccine and Shingles

A new study from researchers at the Centers for Disease Control and Prevention (CDC) has found that use of the chickenpox vaccine during childhood does not appear to be related to the rising incidence of herpes zoster (HZ) in individuals older than 65 years of age.

“The findings from this study are reassuring that the US varicella vaccination program has not, in fact, led to an increase in zoster incidence in older adults and that we should continue to fully vaccinate children against varicella,” said lead author Craig M. Hales, MD, MPH, Division of Viral Diseases, National Center for Immunization and Respiratory Diseases, CDC, Atlanta, GA.

The universal chickenpox vaccine started being used in the United States in 1996. Since its introduction, there have been concerns that implementing a universal varicella vaccination program for children could lead to an increase in HZ incidence, explained Hales.

“These concerns stem from the idea that when we are exposed to children with varicella, we may get a natural boost to our immunity against zoster,” he said.

The results of previous studies examining the association between a person’s exposure to chicken pox and his or her risk of HZ have been conflicting. Hales offered a suggestion as to why this study did not show this effect.

“Perhaps exposure to children with varicella doesn’t actually boost our immunity to zoster,” he said. Alternatively, “if our immunity is, in fact, boosted by exposure to varicella, perhaps exposure in older adults isn’t frequent or intense enough for this effect to occur; or perhaps the effect is too small or too short-lasting to detect it with this type of study.”

Researchers conducted a retrospective study of 2,848,765 Medicare beneficiaries (aged >65 years) which evaluated annual HZ incidence using Medical claims data from 1997 through 2010  They also calculated rate ratios for HZ incidence by age, sex, and race/ethnicity and the association between HZ incidence and state-level varicella vaccination coverage.

The annual rate of HZ incidence increased by 39% during the study period (from 10 per 1000 person-years in 1992 to 13.9 per 1000 person-years in 2010), but there were no statistically significant changes detected in the rate of increase after the introduction of the chicken pox vaccine. Researchers also found that HZ incidence did not vary by state varicella vaccination coverage.

According to Hales, another important finding of this study is that HZ incidence appears to be increasing, “yet we do not have a satisfactory explanation for this increase,” he said.

“More research is needed on the pathophysiology and epidemiology of zoster to understand why one-quarter to one-third of the population develops zoster at some point during their lives while the majority never does,” Hales told Consultant360. “Understanding this will also help us understand why zoster incidence is increasing.”

In the meantime, he pointed out that there is a CDC-recommended HZ vaccine for adults aged 60 years and older; however, only 16% of adults in this age group have received it as of 2011.

“The zoster vaccine is an effective but underutilized tool we can use to help prevent pain and suffering in older patients,” said Hales. “We need to redouble our efforts to vaccinate older adults to help protect them against the devastating effects of zoster and its complications.”

He suggested that healthcare providers who do not carry the HZ vaccine can also refer their patients to a pharmacy or another provider who can administer the vaccine.

This research is available in the Annals of Internal Medicine.

-Meredith Edwards White

Reference

Hales CM, Harpaz R, Joesoef MR, Bialek SR. Examination of links between herpes zoster incidence and childhood varicella vaccination. Ann Intern Med. 2013 Dec 3;159(11):739-745. doi: 10.7326/0003-4819-159-11-201312030-00006.