The 20th century witnessed remarkable improvements in human health, largely driven by advancements in public health, medical technology, and disease control. The burden of infectious diseases was gradually reduced through widespread initiatives and sanitation efforts, including vaccination campaigns, water treatment, increased public awareness, and targeted eradication programs (Armstrong et al., 1999). These efforts led to significant improvements in overall population health. Recently, a growing body of literature has begun to evaluate the long-term impacts of these public health interventions from the early 20th century, providing evidence of their lasting benefits. These studies suggest that early-life and childhood exposure to these interventions are associated with improved human capital, labor market outcomes, cognitive ability, and mortality later in life (Anderson et al., 2019, D.M. 2022; Beach et al., 2016; Case et al., 2002, 2005; Case and Paxson, 2009; Cutler and Miller, 2005, D. 2022; Noghanibehambari and Fletcher, 2024d).

In this paper, we focus on a large-scale targeted eradication program in the US South and explore its lasting impacts on individuals’ longevity in old age. Specifically, we examine the hookworm eradication campaign that was initiated by the Rockefeller Sanitary Commission (RSC) in 1910. The RSC provided substantial funding, donating over $1 million to support the hookworm eradication campaign, facilitating widespread treatment, education, and infrastructure improvements in the US South.

Hookworm disease is caused by the parasitic worms Necator americanus and Ancylostoma duodenale, which typically enter the body through the skin, usually the feet, and reside in the intestines, where they feed on blood. This results in chronic anemia, malnutrition, and impaired physical and cognitive development, particularly in children. However, before 1910, there was limited understanding of the disease and its effects. The realization that many health problems among Southerners could be traced to hookworm disease was a key factor motivating the RSC’s eradication campaign.

A narrow strand of research examines the effects of this campaign on the social and economic outcomes of affected areas in the short term and long term. For instance, Bleakley (2007) shows that cohorts who were exposed to hookworm eradication during childhood have higher education and literacy during adulthood. These individuals revealed higher earnings in 1940 and enjoyed higher returns to schooling for their earnings.1 Fox & Grigoriadis (2022) find that the human capital improvements linked to the Rockefeller hookworm campaign appear only in counties that later adopted cooperative public–private county health organizations, while areas relying on independent local efforts show little or negative effects, indicating that sustained institutional cooperation is central to the observed gains. Bleakley & Lange (2009) provide evidence that the sharp increase in the human capital of children due to hookworm eradication was accompanied by reductions in fertility, suggesting a quality-quantity trade-off in parental fertility decisions. Nonetheless, fewer studies have explored the longer-run impacts of this large-scale eradication program on health and mortality outcomes. The current study fills this gap in the literature.

We employ data from the Social Security Administration death records linked to the 1940 full-count census and implement a two-way fixed effect estimation strategy to compare longevity outcomes of individuals who were born in different years relative to the starting year of the campaign in counties with differential intensity of treatment imposed by the RSC initiative. We find intent-to-treat effects of exposure during in-utero and early-life due to the eradication campaign of about a 1.3-month increase in longevity. We find larger impacts among nonwhites, children of illiterate parents, and those born in urban areas. Supplementary analyses using the 1940 census and World War II enlistment data provide suggestive evidence of improvements in education, wage income, and cognitive ability. We do not find discernible impacts of exposure during childhood despite the findings of previous literature on the improvements in their educational outcomes and the potential role of education on health and longevity. Further, we show that our findings do not pick up on differential characteristics of treated cohorts, do not reflect a trend in longevity among older children and adults, and are robust to a wide array of alternative specifications, subsamples, functional forms, and estimation strategies.

Moreover, we provide evidence of dynamic complementarity in the effects of hookworm eradication on longevity. Our findings show that the effects are more pronounced in counties that were exposed to the Rosenwald school construction movement. Such complementarity is specifically present among nonwhites, the target population of the Rosenwald school construction projects. Additionally, states with more stringent child labor laws also experienced larger improvements in longevity outcomes, suggesting that educational resources and policies played a critical role in strengthening the benefits of hookworm eradication.

This study makes three important contributions to the literature. First, it adds to the small literature that evaluates the impacts of the hookworm disease on outcomes, and more specifically, the RSC hookworm eradication campaign (Bleakley, 2007; Bleakley and Lange, 2009; Henderson, 2018; Ness et al., 2020; Sakti et al., 1999). Our study is among the first studies to explore the benefits of the program on later-life longevity outcomes. Concurrently, Lawton (2025) uses a similar natural-experiment design and finds that early-life deworming increased adult lifespan by approximately 2–3 months. Using linked 1940 Census–mortality data and a broader death window, we estimate longevity gains of comparable magnitude, while additionally documenting heterogeneity across socioeconomic and institutional environments and exploring complementary mechanisms.

We should note that although longevity and mortality are extreme proxies of health, they are more accurately measured than many subjective measures of health. Moreover, studies show strong correlations between longevity and other economic outcomes (Blackburn and Cipriani, 2002).

Second, our study connects to and extends the broader literature on deworming interventions in developing countries. Seminal work by Miguel & Kremer (2004) demonstrates large positive effects of school-based deworming campaigns on health and educational outcomes in Kenya, while later studies explore long-run impacts. Specifically, Baird et al. (2016) show that a school-based deworming program in Kenya led to substantial long-run gains in labor supply, educational attainment, and living standards among treated individuals, with an estimated financial internal rate of return of 32 %. However, despite the passage of time, debate remains regarding the effectiveness and broader relevance of mass deworming programs, particularly with respect to their long-run health and economic impacts. Our analysis complements and strengthens this literature by providing evidence from a mass deworming campaign implemented in an earlier era and a different context.

Third, our study adds to the literature that examines the role of early-life disease environment on later-life health and mortality outcomes. Several studies of this literature proxy disease environment with county/state-level infant mortality rates and document correlations with later-life cognition, health, and mortality (Almond et al., 2012; Bozzoli et al., 2009; Case and Paxson, 2009; Noghanibehambari and Fletcher, 2023c). Other studies in this literature exploit natural experiment settings. Specifically, they examine the impacts of outbreaks, such as the polio pandemic of 1916 and the Spanish flu pandemic of 1918–1919, on later-life education, disability, and mortality (Almond, 2006; Almond and Mazumder, 2005; Meyers and Thomasson, 2021; Noghanibehambari and Fletcher, 2023d). However, the evidence of the long-term impacts of disease eradication and public health campaigns of the early 20th century is limited. Our study contributes to this line of research. Third, our study also contributes to the recently growing literature that evaluates the impacts of early-life conditions and exposures on later-life mortality and longevity outcomes (Aizer et al., 2016; Bengtsson and Lindström, 2000; Elo and Preston, 1992; J. Fletcher and Noghanibehambari, 2024; Gluckman et al., 2008; Hayward and Gorman, 2004; Lindeboom et al., 2010; Lindeboom and Van Ewijk, 2015; McEniry, 2013; Myrskylä, 2010; Noghanibehambari et al., 2024; Noghanibehambari and Fletcher, 2023a, 2023b, 2024b; Pudrovska and Anikputa, 2014; Van Den Berg et al., 2006; Vu et al., 2023). Although several diseases of the early 20th century have been eradicated, many developing countries remain burdened by a variety of communicable and infectious diseases (Alirol et al., 2011; Boutayeb, 2010). These countries are experiencing similar social and economic developmental stages to those of the US in the early 20th century. Therefore, the results of this paper have policy implications for policymakers in these countries, as well as for international advocates and initiatives aiming to improve population health outcomes and eradicate diseases. Recent pandemics, such as the Ebola virus outbreak, the Middle East Respiratory Syndrome outbreak, and the COVID-19 pandemic, suggest that the spread of infectious diseases is not confined to developing countries in a globalized world (Baker et al., 2021). Therefore, understanding the long-term impacts of early-life disease environments remains highly relevant today.

The rest of the paper is organized as follows. Section 2 introduces data sources and the process of sample selection. Section 3 discusses the econometric method. Section 4 reviews the results. Section 5 discusses mechanism channels. We conclude the paper in Section 6.