# Trends in the Incidence of Ramsay Hunt Syndrome and Zoster Sine Herpete Following the Introduction of Routine Varicella Vaccination in Hokkaido, Japan

## TL;DR

This study found that after routine varicella vaccination in Japan, younger adults had a higher risk of developing HZ-related facial palsy, including Ramsay Hunt syndrome and zoster sine herpete.

## Contribution

The study reveals a significant increase in HZ-related facial palsy among 15-29-year-olds post-varicella vaccination, highlighting a new clinical trend.

## Key findings

- The overall proportion of HZ-related facial palsy did not change significantly after routine varicella vaccination.
- Among patients aged 15-29 years, the proportion of HZ-related facial palsy increased significantly from 38.9% to 63.3%.
- Younger patients had approximately 2.7 times higher odds of developing HZ-related facial palsy after vaccination.

## Abstract

Background: Routine varicella vaccination was introduced in Japan in October 2014. A large-scale epidemiological study conducted in Miyazaki Prefecture subsequently reported a marked increase in the incidence of herpes zoster (HZ) among the child-rearing population aged 20-40 years following this introduction.

Objective: This study aimed to investigate long-term trends in the incidence of HZ-related facial palsy, Ramsay Hunt syndrome (RHS) and zoster sine herpete (ZSH), among patients with acute peripheral facial palsy (APFP) aged 15 years or older, treated at a single institution in Hokkaido, Japan, over a 15-year period (2007-2022), and to compare the proportions before and after the introduction of routine varicella vaccination.

Methods: This retrospective cohort study included 641 patients (15 years old or older) diagnosed with APFP, including Bell’s palsy, ZSH, and RHS, between July 2007 and December 2022 at a single institution in Hokkaido, Japan. Varicella-zoster virus (VZV) reactivation was diagnosed using an enzyme-linked immunosorbent assay with paired serum samples. The ratio of HZ was defined as the proportion of ZSH and RHS cases among all APFP patients.

Results: VZV reactivation was confirmed in 219 of 641 patients (34.2%). The proportion of HZ-related facial palsy was 33.6% (102/304) before the introduction of routine varicella vaccination and 34.7% (117/337) afterward, showing no significant overall change. However, among patients aged 15-29 years, the proportion of HZ significantly increased from 38.9% (14/36) before vaccination to 63.3% (19/30) after vaccination. This corresponds to an odds ratio of 2.714 (95% CI: 1.009-7.301), indicating that individuals in this age group had approximately 2.7 times higher odds of developing HZ-related facial palsy in the postvaccination period compared with the prevaccination period. The chi-square statistic (χ² = 3.910) and p-value (p = 0.048) further support that this increase is statistically significant.

Conclusions: Although the overall incidence of HZ-related facial palsy among APFP patients did not change significantly after the implementation of routine varicella vaccination in 2014, a marked increase was observed in younger patients aged 15-29 years. These findings suggest a need for heightened clinical awareness of VZV reactivation in young generation presenting with APFP in Hokkaido, Japan.