Abstract
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%CrI: 10-13), 43 (90%CrI: 33-53), 23,319 (90%CrI: 15,312–33,139), 3,762 (90%CrI: 1,650–4,629) and 165 (90%CrI: 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.
Key words: Herpes zoster (HZ), post-herpetic neuralgia (PHN), vaccines, mathematical model, number needed to vaccinate
Résumé
Contexte
Un essai clinique a montré qu’un vaccin vivant atténué contre le virus varicelle-zona est efficace contre l’herpès zoster (zona) et l’algie post-zostérienne. Nous avons cherché à estimer le nombre de personnes qu’il faudrait vacciner (NPV) pour prévenir divers problèmes liés au zona.
Méthode
Nous avons élaboré un modèle de cohorte pour la morbidité, l’utilisation des ressources en soins de santé et la mortalité associées au zona. Des données basés sur la population canadienne ont servi à estimer l’incidence selon l’âge, les hospitalisations, les années de vie perdues pondérées par la qualité, ainsi que la mortalité. Le NPV désigne le nombre de personnes à vacciner pour prévenir la manifestation d’un problème lié au zona au cours de la vie. Nous avons étudié des sujets d’âge différent lors de la vaccination et effectué une analyse de sensibilité probabiliste.
Résultats
Chez les sujets de 65 ans, nous avons estimé que le NPV (efficacité du vaccin contre le zona=63 %, efficacité du vaccin contre l’algie post-zostérienne=67 %, sans baisse de l’immunité) s’établirait à 11 pour prévenir un cas de zona (intervalle de crédibilité [ICr] à 90 %, 10-13), à 43 pour prévenir un cas d’algie post-zostérienne (ICr à 90 %, 33-53), à 23 319 pour prévenir un décès attribuable au zona (ICr à 90 %, 15 312–33 139), à 3 762 pour prévenir une année de vie perdue (ICr à 90 %, 1 650–4 629), et à 165 pour prévenir une année de vie perdue pondérée par la qualité (ICr à 90 %, 105-197). Ces résultats étaient particulièrement sensibles à la durée de la protection vaccinale et à l’âge du sujet lors de la vaccination.
Discussion
Même si le vaccin n’est efficace que dans une proportion de 50 à 70 %, il faudrait vacciner relativement peu de sujets pour prévenir le zona et l’algie post-zostérienne, un résultat qui s’explique par la forte incidence de ces deux maladies chez les personnes âgées. Il est clair que le principal avantage du vaccin contre le zona est de prévenir la morbidité causée par la douleur (mesurée en années de vie perdues pondérées par la qualité) plutôt que la mortalité.
Mots clés: herpès zoster (zona), algie post-zostérienne, vaccins, modèle mathématique, nombre de personnes qu’il faudrait vacciner
Footnotes
Acknowledgements and financial disclosure: Dr. Brisson was an employee of Merck Frosst Canada Ltd. during the preliminary analysis. He is now associate professor at Laval University. He has consulted for Merck Frosst and has received reimbursement for travel expenses from GlaxoSmithKline. The study was funded by Merck Frosst. The contract stipulates that Dr. Brisson has absolute discretion over the contents of the publication.
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