A working paper with Justin Sandefur, Sarah Dykstra and Amanda Glassman. Since 2001, an aid consortium known as Gavi has accounted for over half of vaccination expenditure in the 75 eligible countries with an initial per capita GNI below $1,000. Regression discontinuity (RD) estimates show aid significantly displaced other immunization efforts and failed to increase vaccination rates for diseases covered by cheap, existing vaccines. For some newer and more expensive vaccines, i.e., Hib and rotavirus, we found large effects on vaccination and limited fungibility, though statistical significance is not robust. These RD estimates apply to middle-income countries near Gavi's eligibility threshold, and cannot rule out differential effects for the poorest countries. There's a policy brief that's an easier read.