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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 towards infectious
disease.
