Direct and Indirect Effects of Vaccines: Evidence from COVID-19
利用一个州内12岁和11岁儿童接种COVID疫苗时间差六个月的微观数据，估计疫苗直接降低80%病例，且对家庭接触者有约四分之三的直接效应大小的间接保护，但对学校同学无此效应。
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.