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Although it is well known that vaccines against many infectious diseases confer positive economic externalities via indirect protection, analysts have typically ignored possible herd protection effects in policy analyses of vaccination programs. Despite a growing literature on the economic theory of vaccine externalities and several innovative mathematical modeling approaches, there have been almost no empirical applications. The first objective of the paper is to develop a transparent, accessible economic framework for assessing the private and social economic benefits of vaccination. We also describe how stated preference studies (for example, contingent valuation and choice modeling) can be useful sources of economic data for this analytic framework. We demonstrate socially optimal policies using a graphical approach, starting with a standard textbook depiction of Pigouvian subsidies applied to herd protection from vaccination programs. We also describe nonstandard depictions that highlight some counterintuitive implications of herd protection that we feel are not commonly understood in the applied policy literature. We illustrate the approach using economic and epidemiological data from two neighborhoods in Kolkata, India. We use recently published epidemiological data on the indirect effects of cholera vaccination in Matlab, Bangladesh (Ali et al., 2005) for fitting a simple mathematical model of how protection changes with vaccine coverage. We use new data on costs and private demand for cholera vaccines in Kolkata, India, and approximate the optimal Pigouvian subsidy. We find that if the optimal subsidy is unknown, selling vaccines at full marginal cost may, under some circumstances, be a preferable second-best option to providing them for free.

A contingent valuation survey was conducted in Kumasi, Ghana, to estimate households' willingness to pay for two types of improved sanitation services: improved ventilated pit latrines and water closets connected to a sewer system. Over 1200 randomly selected households throughout the city were interviewed. Most households were willing to pay more for improved sanitation service than they were currently paying for their existing sanitation system (mostly public and bucket latrines), but in absolute terms the potential revenues from households are not large, of the order of US$1.40 per household per month (about 1-2% of household income). The results of the study confirm the conventional wisdom that conventional sewerage is not affordable to the vast majority of households without massive government subsidies. On the other hand, it appears that only modest subsidies are required to achieve relatively high levels of coverage with on-site sanitation (improved ventilated pit latrines). This is because improved ventilated pit latrines are much cheaper than conventional sewerage and because most households are willing to pay about as much for a ventilated pit latrine as for a water closet connected to a sewer. Several tests were conducted to check the accuracy of respondents' answers to contingent valuation questions. The findings indicate that contingent valuation surveys can be successfully carried out in cities in developing countries for public services such as sanitation and that reasonably reliable information can be obtained on household demand for different sanitation technologies. al., 1987].Evidence on the accuracy of the CVM in developing countries is much more limited, but the few available studies suggest that contingent valuation (CV) surveys can be successfully implemented in this context as well [Whittington et al.A study of water vending and willingness to pay for water in Onitsha, Nigeria, Worm Devel., 19(2/3), 179-198, 1991.

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