Direct and Indirect Effects of Vaccines: Evidence from COVID-19

Seth Freedman, Daniel W. Sacks, Kosali Simon and Coady Wing

American Economic Journal: Applied Economics, 2026, vol. 18, issue 1, 1-43

Abstract: We estimate direct and indirect vaccine effectiveness and assess how far the infection-reducing externality extends from the vaccinated, a key input to policy decisions. Our empirical strategy uses nearly universal microdata from a single state and relies on the six-month delay between 12- and 11-year-old COVID vaccine eligibility. Vaccination reduces cases by 80 percent, the direct effect. This protection spills over to close contacts, producing a household-level indirect effect about three-fourths as large as the direct effect. However, indirect effects do not extend to schoolmates. Our results highlight vaccine reach as important to consider when designing policy for infectious disease.

JEL-codes: D62 H51 H75 I12 I18 J13 (search for similar items in EconPapers)
Date: 2026
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Working Paper: Direct and indirect effects of vaccines: Evidence from COVID-19 (2022)
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DOI: 10.1257/app.20230717

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