Estimating the number needed to vaccinate to prevent herpes zoster-related disease, health care resource use and mortality.

BACKGROUND A clinical trial has shown that a live-attenuated varicella-zoster virus vaccine is effective against herpes zoster (HZ) and post-herpetic neuralgia (PHN). The aim of the study was to estimate the number needed to vaccinate (NNV) to prevent HZ-related outcomes. METHODS A cohort model of HZ associated disease, health care resource use and mortality was developed. Canadian population-based data were used to estimate age-specific incidence, hospitalization, quality-adjusted life-year (QALY) lost and mortality. NNV was calculated as the number of individuals needed to be vaccinated to prevent a specific HZ-related outcome during their lifetime. Different ages at vaccination were examined and probabilistic sensitivity analysis was performed. RESULTS For 65 year olds, the NNV (HZ vaccine efficacy=63%, PHN vaccine efficacy=67%, no waning) to prevent a case of HZ, a case of PHN, a HZ death, a life-year lost and a QALY lost is estimated to be 11 (90% Crl: 10-13), 43 (90% Crl: 33-53), 23,319 (90% Crl: 15,312-33,139), 3762 (90% Crl: 1650-4629) and 165 (90% Crl: 105-197), respectively. Results were most sensitive to the duration of vaccine protection and the age at vaccination. DISCUSSION The predicted NNV to prevent HZ and PHN are low even though vaccine efficacy is between 50-70%, which reflects the high incidence of these diseases among older adults. Results clearly show that the main benefit of HZ vaccination is prevention of morbidity caused by pain (as measured by QALYs lost) rather than mortality.