Eradicating diseases: The effect of conditional cash transfers on vaccination coverage in rural Nicaragua
Introduction
Reducing the burden of illness and mortality from preventable diseases through vaccination is a key component of public health policy. Impressive achievements have been made worldwide; for example, smallpox was eradicated in 1977 and global vaccination rates reached 75% against the major childhood diseases in the mid-1990s.1 Presently, efforts are under way to eradicate polio and many countries are working to eliminate measles (Quadros et al., 2003, Miller et al., 2006).2 Though eradication is costly, the long-term financial gain can be large. For example, the payoff for eradicating polio is estimated to be as high as $ 1 billion per annum, since it eliminates the need for future prevention and treatment of the afflicted and avoids their potentially lost economic contributions to society (GPEI, 2003, Khan and Ehreth, 2003).
Despite these successes, two million children die each year from vaccine preventable diseases (WHO, 2008). This is in part because global vaccination levels for major childhood diseases have been static for a decade (Foster et al., 2006), leaving approximately 26 million children worldwide inadequately protected (UNICEF, 2008). Even the better performing regions are expected to plateau below 90% coverage rates for the third dose of the diphtheria–pertussis–tetanus vaccine (DPT3), a standard indicator for overall vaccination program effectiveness (WHO, 2006). Moreover, high average coverage rates hide large disparities both across and within countries (WHO/UNICEF, 2007).
To eradicate diseases such as measles, vaccination coverage rates close to 95% are needed (Barrett and Hoel, 2003). With the experience of the past decade in mind, however, it would appear that new strategies may be required to reach such levels. Geoffard and Philipson (1997) argue that the “demand side” is critical for eradication because as the prevalence of a disease declines so, too, does the demand by individuals to be vaccinated against that disease. This potentially allows the disease to resurge. Their theoretical model demonstrates that even traditional price subsidies (such as free vaccination at health facilities) and mandatory vaccination programs may be limited in their ability to eradicate a disease. Xie and Dow (2005) explore the supply and demand sides of vaccination empirically and find that both supply-side factors (e.g., the price of vaccine services), as well as demand-side factors (e.g., maternal education) are important household-level determinants of vaccination. Most national vaccination strategies, however, focus on the supply of vaccinations, including taking services directly to the household during mass vaccination campaigns. Demand-side strategies tend to be limited to awareness raising or social mobilization campaigns, which may miss some important groups such as children of poorly educated mothers. As a result, stronger demand-side incentives may be needed to increase vaccination coverage to the levels needed for eradication.
We examine how a conditional cash transfer (CCT) program, which includes a substantial demand-side component, affects vaccination rates in rural Nicaragua. Prior to the program's implementation, Nicaragua, with the lowest GDP per capita in Central America, had vaccination rates below 90%. It thus provides a low-income setting to assess whether CCTs can boost coverage to 95%. The analysis uses a randomized experimental evaluation of a pilot CCT program, the Red de Protección Social (RPS), to provide double-difference estimates of the program's effects. After 2 years of program operation (2000–2002), there were large effects, especially for typically hard to reach populations such as children whose mothers were less educated or who lived further away from a health facility. The program pushed coverage rates for children 12–23 months old above 95% for DPT3 in the treatment group, compared with 85% in the control group. In contrast, coverage for the same age group for DPT3 for the country as a whole was 83% when RPS began in 2000 and had reached only 86% by 2005 (WHO/UNICEF, 2007).
Section snippets
Government vaccination programs in Nicaragua
The Ministry of Health in Nicaragua has a two-pronged vaccination strategy: to provide vaccinations at government health facilities and to hold vaccination campaigns which typically take vaccines to a child's house. Each year between 1999 and 2002, two, month-long vaccination campaigns against all the major childhood diseases were conducted. The government does not rely only on the provision of vaccines at health facilities because there is incomplete coverage of the population and because such
Evaluation design
A 2000–2002 evaluation for RPS was implemented based on a randomized, locality-based intervention in 42 localities. The randomization took place at a public event in which representatives from the localities, the Government of Nicaragua, the Inter-American Development Bank, the International Food Policy Research Institute and the media were present. To ensure that the selection of localities into treatment and control groups was well stratified by wealth, a poverty index was created for each
Methods and empirical model
We estimate the effect of RPS on vaccination coverage for children under three. We evaluate whether a child was vaccinated with BCG, MCV, OPV3, DPT3, and if the child was fully vaccinated with all four vaccines (FVC) and exploit the random assignment to create a control group to examine the counterfactual. In this section, we provide evidence that the randomization led to well-balanced treatment and control groups and then present the main empirical methods.
The effect of RPS on vaccination
First, we present results for children under three based on the survey data and then replicate those results using the administrative data for all but the 24–35-month olds. We then incorporate information on the distance between treatment and control localities to explore possible spillover effects, considering each of the two datasets in turn. Finally, in Section 6, we merge the two datasets together at the individual level, to explore potential measurement error biases.
Table 4 reports the
Measurement error
Several studies have shown that vaccination coverage based on mother's recall rather than actual vaccination cards is biased downwards, and the extent of the bias may be greater for multiple dose vaccines (Valadez and Weld, 1992, Suarez et al., 1997, Langsten and Hill, 1998). At baseline, 24% of households in the survey data did not show a vaccination card, so coverage rates for the sample may be underestimated. If the coverage rates are underestimated in each survey round, and the measurement
Discussion
We find positive, fairly substantial, and significant impacts of the Nicaraguan conditional cash transfer program, RPS, on vaccination coverage for selected vaccines, age groups and sub-populations. Effects were particularly large for those sub-populations that are traditionally harder to reach—children who live further away from a health facility or whose mothers are less educated. In terms of achieving eradication, on-time vaccination coverage in the treatment group was close to or greater
Acknowledgements
We thank Logan Brenzel, as well as PAHO and the Ministry of Health of Nicaragua for providing background information and Alexis Murphy and Tom Dickinson for excellent research assistance in the preparation of the data for this paper. David Coady, Will Dow, Richard Frank, Dan Gilligan, Norbert Schady, T. Paul Schultz, an anonymous referee, and participants at the Population Association of America and the Midwest International Development Economics Conferences for their comments. The generous
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