Summary of the NACI Update on Herpes Zoster Vaccines.

Background: Steep increases in herpes zoster (HZ) incidence, hospitalization due to HZ and the risk of post-herpetic neuralgia as a complication of HZ occur in people over 50 years of age. Two HZ vaccines are currently authorized for use in those 50 years of age and older in Canada: a live attenuated zoster vaccine (LZV) authorized in 2008; and a recombinant subunit vaccine (RZV) authorized in October 2017.

Objectives: To review current evidence and develop guidance on whether the previously authorized LZV (Zostavax) and/or the recently authorized RZV (Shingrix) vaccine should be offered to Canadians 50 years of age and older: 1) at a population-level, in publicly funded immunization programs; and 2) at an individual-level, to individuals wishing to prevent HZ, or by clinicians wishing to advise individual patients about preventing HZ.

Methods: The National Advisory Committee on Immunization (NACI) Herpes Zoster Working Group developed a predefined search strategy to identify all eligible studies, assessed their quality, and summarized and analyzed the findings. A Cost Utility Analysis of LZV and RZV was also conducted from a health care system perspective. Recommendations were proposed according to NACI's evidence-based process. The strength of these recommendations was defined, and the Grade of evidence supporting them was identified. In light of the evidence, the recommendations were then considered and approved by NACI.

Results: Five recommendations were developed for public health and individual-level decision-making. 1) RZV to populations/individuals >50 years of age without contraindications (Strong NACI Recommendation, Grade A evidence). 2) RZV to populations/individuals >50 years of age without contraindications who have previously been vaccinated with LZV (Strong NACI Recommendation, Grade A evidence). Re-immunization with two doses of RZV may be considered one year after LZV (Discretionary NACI Recommendation, Grade I evidence). 3) RZV to populations/individuals >50 years of age without contraindications who have had a previous episode of HZ (Strong NACI Recommendation, Grade B evidence). Immunization with two doses of RZV may be considered one year after the HZ episode (Discretionary NACI Recommendation, Grade I evidence). 4) LZV for immunocompetent populations/individuals >50 years of age without contraindications when RZV is contraindicated, unavailable or inaccessible (Discretionary NACI Recommendation, Grade A evidence). 5) RZV (not LZV) in immunocompromised adults >50 years of age on a case-by-case basis (Discretionary NACI Recommendation, Grade I evidence).

Conclusion: Both vaccines have been shown to be safe and immunogenic and to reduce the incidence of HZ and post-herpetic neuralgia. Vaccine efficacy of LZV against HZ decreases with age at, and time since vaccination. The vaccine efficacy of RZV remains higher and appears to decline more slowly than vaccine efficacy of LZV across all age groups. Both vaccines are cost-effective in those 50 years of age and older compared with no vaccination, especially in those 65-79 years of age. RZV is more cost-effective than LZV.