Assumptions were confusing
BMJ 1995; 310 doi: https://doi.org/10.1136/bmj.310.6976.402 (Published 11 February 1995) Cite this as: BMJ 1995;310:402
- Pierre Van Damme,
- Eddy Van Doorslaer,
- Guy Tormans,
- Philippe Beutels
- Research fellow Professor of health economics Research fellow Research fellow Epidemiology and Community Medicine, University of Antwerp, B-2610 Antwerp, Belgium
EDITOR,—We have performed economic evaluations of prophylaxis against hepatitis A in travellers, and two of R H Behrens and J A Roberts's main conclusions1 are in line with our findings2 3—namely, that hepatitis A vaccination is not cost saving for the average traveller and that vaccination becomes more cost effective than immunisation with human immunoglobulin when the expected frequency of travel exceeds two occasions in the next 10 years. Despite this agreement, we have some difficulties with several assumptions and statements made in the article.
Firstly, the authors state that the cost-benefit ratio of (passive and active) immunisation increases as the seroprevalence reduces to 9.7% (instead of 30%). This seems nonsensical: it can never be the case that the attractiveness of a preventive action decreases when the proportion of susceptible subjects increases since costs remain the same but benefits increase as more infections can be prevented. Secondly, there is substantial confusion regarding the required threshold incidence (or risk) of hepatitis A that would give a cost-benefit ratio of one. The authors state that this would occur with 1550 cases annually. This is about six times their reported number of cases of 288 but only three times the “corrected” number of 576 in table I. Nevertheless, the authors say that even if the assumed incidence of 0.05% increased sixfold to the incidence of 0.3% per visit reported for Swiss travellers “the costs would still exceed the benefits by a significant amount.” How can these two contradictory statements be reconciled? Thirdly, the authors have performed a cost-benefit analysis but use the terminology carelessly when they say that hepatitis A vaccination is not cost effective (in the abstract) or even is inefficient (in the discussion) when they mean not cost saving.
Finally, we think that it is important to specify further the indications for prophylaxis against hepatitis A and agree that it is necessary to design “a suitable protocol which would target high risk non-immune groups.” We have derived some recommendations regarding optimal choices in various circumstances based on a cost-effectiveness analysis elsewhere.4