Reduction in Herpes Zoster Antiviral Use Since the Introduction of the Live-Attenuated Zoster Vaccine on Australia's National Immunisation Program: A Population-Based Study from 1994 to 2019.

INTRODUCTION: Zostavax, the live-attenuated vaccine used to prevent herpes zoster (HZ), has been available to individuals aged 70 and 71-79 years (phased catch-up) via Australia's National Immunisation Program (NIP) since 2016. There are limited data characterising the incidence of HZ at the level of the Australian population. National prescription data for antivirals used to treat HZ may be used as a proxy for HZ incidence. We aimed to examine trends in antiviral prescriptions supplied for the treatment of HZ in Australia pre- and post-2016, and to assess whether Zostavax's inclusion on the NIP correlated with a reduction in HZ antiviral prescription rates.

METHODS: Using the Australian Pharmaceutical Benefits Scheme and Repatriation Pharmaceutical Benefits Scheme prescribing data, we analysed antiviral prescriptions supplied for the treatment of HZ Australia-wide between 1994 and 2019. Annual prescription rates were calculated, and trends and changes in HZ antiviral use were explored descriptively and using Poisson models.

RESULTS: HZ antiviral prescription rates increased 2.6-fold (160%) between 1995 and 2015 [25.4 (95% CI 25.2, 25.6) and 65.3 (95% CI 64.9, 65.6) prescriptions per 10,000 people, respectively], and then decreased 0.45-fold (55%) between 2016 and 2018 [60.9 (95% CI 60.6, 61.2) and 27.5 (95% CI 27.3, 27.9) prescriptions per 10,000 people, respectively]. The prescription rate for the antiviral famciclovir restricted specifically for treating HZ in immunocompromised individuals increased 8.5-fold (750%) between 2006 (year first listed) and 2019 [0.3 (95% CI 0.3, 0.3) and 2.5 (95% CI 2.4, 2.6) prescriptions per 10,000 people, respectively].

CONCLUSION: The introduction of the live-attenuated HZ vaccine on Australia's formal national vaccination program was associated with a reduction in HZ antiviral prescription rates within the Australian population. The data suggest that the introduction of Shingrix, the non-live subunit zoster vaccine, may also be associated with a similar reduction in HZ antiviral prescriptions used to treat the immunocompromised, as well as the general population, given its accepted greater efficacy over Zostavax.