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

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.