Cost-effectivness and meningococcal vaccine
There’s a story in the Herald arguing for mass vaccination in NZ against group C meningococcal disease. There’s a good case for the vaccination — it’s a really nasty disease and there aren’t any other good treatment or prevention approaches — but I don’t see how the cost-effectiveness claims in the story can be right.
Dr Gravatt is quoted as saying there would be zero net medical cost for the vaccination program
Dr Gravatt estimated the net cost of vaccinating children at 12 months and again at 18 years would be zero for each “quality-adjusted” year of life saved at a vaccine price of $25 to $40 per dose. The listed prices were around $43 to $87, but discounts would be likely in a bulk contract.
He refers to a British vaccine study — which one isn’t specified. However, there are cost-effectiveness analyses of the whole British group C meningococcal vaccination program (they vaccinate against group C but not group B, the opposite of NZ). One, from 2002, estimates a cost per life year saved of £6259. The second, from 2006, considers a wider range of possible vaccination programs: for the one that’s most similar to what Dr Gravatt proposed it estimates net medical costs of £9082 per quality-adjusted life year, and for the cheapest one,
£3653 £2760 (update)per quality-adjusted life year. And that’s assuming the vaccine costs only £12 per dose, and in a country where group C meningococcal disease was slightly more common than it is here.
Another way to look at it: there are about 60000 births per year in NZ, so after the initial catch-up phase we’d be paying for 120000 doses per year. Even at $25 per dose, that comes to $3 million per year. According to the Herald’s story there are about 25 cases per year, so for the vaccination to be cost-neutral even at this lowest suggested price, the average disease case would have to cost the healthcare system $120000. That’s more than ten times what the UK cost-effectiveness study estimated (roughly £4000) including both the immediate cost of treating the disease and the cost of treating the long-term effects.
The vaccine looks to be a lot more cost-effective than, say, the prostate cancer drug that Campbell Live was pushing last week, and because herd immunity is important for this disease, there’s a relatively stronger case for vaccinating everyone, but that would be because the cost is worth it, not because the cost is zero.
Updates, including a lot more technical detail:
[Update: Dr Gravatt’s letter with his calculations is up at the New Zealand Medical Journal, unfortunately for subscribers/institutions only. The difference between the UK conclusions and his numbers is in a big difference in estimated total cost for long-term care of complications in survivors. I don’t yet understand why.]
Update again: Ok. Comparing Dr Gravatt’s calculations with the 2002 UK analysis I now understand the differences in long-term care costs. The minor difference is in the assumed proportion of people needing long-term institutional care: the UK paper assumes 10% of 7% of cases, ie, 0.7%, and Dr Gravatt is using 2.1%.
The second difference is more important: the UK paper is discounting costs and benefits in the future, at a rate of 3% per year and Dr Gravatt isn’t discounting. It’s pretty uncontroversial that monetary costs and savings should be discounted: even after inflation-adjustment, it’s better to have money now than later. That means the current value of a lifetime’s care for a disabled person is less than the total of the yearly payments. Since the costs of vaccination are incurred now and the cost savings are realised long into the future, the discount rate matters. Using Dr Gravatt’s figures for rate of sequelae and discounting just the future monetary costs at 3% (the UK rate) gives a present value of costs from not vaccinating that’s about half the undiscounted costs, suggesting a cost-effective but not cost-neutral treatment. Pharmac’s discount rate is 3.5%, which would give a slight further reduction in the estimated cost savings.
The UK paper also discounted the benefits (life years) in the future. Discounting non-monetary benefits (life years saved) is fairly standard but is controversial; fortunately I’m only addressing the monetary costs so I don’t need to take a position on discounting the QALYs.
The second UK paper gives a very much lower present value of costs for long-term sequelae. That’s the paper I was initially relying on, and I don’t understand why it’s so different. The difference in long-term costs doesn’t have a huge impact on the conclusion, because the acute costs are high and the long-term costs are discounted, but it’s still confusing. I’ve emailed the author to ask.
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »