The cost-effectiveness of introducing a varicella vaccine to the New Zealand immunisation schedule

This study examined the cost-effectiveness of adding a varicella vaccine to an existing childhood immunisation schedule relative to a counterfactual where the varicella vaccine is available on a user-pays basis (the current New Zealand situation). The costs and consequences of chickenpox in an annual cohort of 57,200, 15-month old children were simulated for a 30-year period. The cohort simulation design captures the 'phasing-in' effects of routine varicella vaccination on the population. From a health care payer's perspective (medical costs only) every dollar invested in a vaccination programme would return NZ $0.67. However, from a societal point of view (which includes the value of work-loss), a vaccination programme would return NZ $2.79 for every dollar invested. To implement a varicella vaccination programme covering 80% of 15-month old children in New Zealand would add more than NZ $1 million in net direct (health care) costs each year. However, the indirect cost savings from reduced losses of work-time exceed NZ $2 million annually. The net average health care cost per child vaccinated over the 30-year modelling period was $54 whereas the cost-savings from work-loss averted averaged $101 per child vaccinated. Total cost-savings to society of $47 per child vaccinated, on average, could be gained from a vaccination programme. The finding that the addition to vaccination costs resulting from a routine programme (including the cost of complications from the vaccine) were greater than the offsetting health care cost savings from reduced incidence of chickenpox were robust to a sensitivity analysis on all assumptions within plausible ranges. Overall cost-effectiveness estimates were most sensitive to assumptions regarding lost work-time, the discount rate, and the price and efficacy of the vaccine. Estimates were relatively insensitive to changes in assumptions regarding health care utilisation.