What is the optimal age for vaccinating against herpes zoster (HZ)?
University of Michigan–led researchers recently tackled that question. Their study, published in the journal Vaccine, notes that cost-effectiveness analyses might provide some insight but have inconsistencies. As a result, they turned to simulation.
Researchers explain that the optimal strategy is important because immunization age has an effect on both the duration of vaccines and their effectiveness. “Therefore, small changes from the optimal age can affect long-term outcomes and produce sub-optimal results,” they write.
“It is estimated that one third of adults will develop herpes zoster (HZ—known commonly as shingles) in their lives and half of adults older than age 85 years will experience or have already experienced HZ,” the study explains. “HZ causes intense pain which can affect quality of life and has a substantial economic burden.”
Two vaccines—HZ live-attenuated vaccine (ZVL) and recombinant zoster vaccine—are available to prevent the disease and are currently the best options for combating HZ, according to the authors, who for this study were focusing only on the strategy of vaccinating with ZVL.
To determine the optimal timing policy for HZ vaccination, the researchers simulated cohorts of men and women and used stochastic dynamic programming to evaluate the decision to vaccinate or to defer each year from age 50 to age 100 years.
In the simulation, if the decision was to defer, the cohort risked developing HZ. If HZ occurred, the cohort was subjected to cost and quality-adjusted life year (QALY) loss for a typical HZ infection, including complications, at that age. If HZ did not occur, the decision was evaluated at the next age.
The model also incorporated the availability of booster vaccines.
Based on the assumption that society is willing to pay $100,000 per QALY, results suggest that the optimal policy is to vaccinate between ages 66 and 77 years for women and between ages 66 and 74 years for men.
Availability of a booster vaccine makes earlier immunization more desirable, according to the study, and women generally have a wider range of ages than men.
The research was touted as the first to examine exactly when the HZ vaccine should be administered.
“It is also the first study, to our knowledge, that used stochastic dynamic programming to examine the question of a second dose for any vaccine,” the authors write. “This research provides the first simple policy on when to vaccinate and re-vaccinate against HZ.”
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