US Incidence Rates of Herpes Zoster and Postherpetic Neuralgia From 1994 to 2018

According to data published in Clinical Infectious Diseases, the incidence rates of herpes zoster (HZ) in age groups for which HZ vaccines are not recommended continue to rise. Investigators believe this finding warrants a review of current vaccine recommendations.

Two HZ vaccines are available, yet the incidence of HZ has been increasing in recent decades. Since the introduction of the vaccines, there have been few studies on the incidence rates of HZ and postherpetic neuralgia (PHN). To investigate whether the incidence rates of both HZ and PHN have continued to rise between 1994 and 2018 in the United States, investigators used data from the deidentified longitudinal administrative claims database, the OptumLabs^® Data Warehouse (OLDW).

They identified 610,766 individuals with HZ (median age, 56.3 years; IQR, 43.0-68.7 years; 59.8% women; and 70.6% white). The incidence of HZ increased between 1994 and 2018 from 286.0 (95% CI, 259.1-312.8) to 579.6 (95% CI, 554.2-605.0) cases per 100,000 person-years, leading to an annual increase of 3.1% (95% CI, 2.5-3.6). However, in individuals ≤20 and >60 years old, the annual HZ incidence rates have decreased since 2007. The overall incidence rate of PHN was 57.5 (95% CI, 56.0-59.0) cases per 100,000 person-years. Investigators also found that the proportion of individuals with HZ who developed PHN was higher from 2007 to 2018 than from 1994 to 2006.

The observational nature of this study meant that it was not possible to determine the cause of the observed changes in HZ and PHN incidence rates. The study was also limited in that HZ vaccination rates were not assessed and no direct association between vaccination rates and incidence could be made. Investigators also noted that, “given the large sample size, there is the risk of minor differences being statistically significant, but conservative statistical analyses were used to mitigate this possibility.”

Furthermore, OLDW captured only individuals enrolled in commercial insurance programs, which means that individuals ≥65 years old, enrolled in Medicare plans, were not included. The study’s generalizability was enhanced by standardizing to the US Census for age and sex and standardizing internally for race/ethnicity. HZ diagnosis was made by a single ICD-9 or ICD-10 code for HZ. Investigators acknowledge that although this, “minimizes the chance of missing cases, there is a risk of overdiagnosis and inflating calculated incidence rates.” They do report, though, that the observed incidence rate estimates are similar to other published rates. Finally, although accuracy of the diagnoses was not verifiable, investigators report that physician diagnoses using ICD-9 codes have previously been shown to have a sensitivity of >90% for HZ and >85% for PHN.

Investigators conclude that the overall incidence rates of HZ and PHN continued to increase in the United States between 1994 to 2018. However, after vaccine introduction in 2007 to 2018, HZ incidence did decrease annually among individuals ≤21 and >60 years old. In this same period, HZ incidence rates continued to rise in individuals 31 to 60 years old. This led investigators to caution that, “it is crucial healthcare providers and policymakers continue to advocate for HZ vaccination and consider revising age recommendations for vaccination to include individuals younger than 50 years of age.”

Reference

Thompson RR, Kong CL, Porco TC, Kim E, Ebert CD, Acharya NR. Herpes zoster and post-herpetic neuralgia: changing incidence rates from 1994 to 2018 in the United States [published online August 23, 2020]. Clin Infect Dis. doi:10.1093/cid/ciaa1185