From August to December 2011, a multidisciplinary group with expertise in mathematical modeling was constituted by the GAVI Alliance and the Bill & Melinda Gates Foundation to estimate the impact of vaccination in 73 countries supported by the GAVI Alliance. The number of deaths averted in persons projected to be vaccinated during 2011-2020 was estimated for ten antigens: hepatitis B, yellow fever, Haemophilus influenzae type B (Hib), Streptococcus pneumoniae, rotavirus, Neisseria meningitidis serogroup A, Japanese encephalitis, human papillomavirus, measles, and rubella. Impact was calculated as the difference in the number of deaths expected over the lifetime of vaccinated cohorts compared to the number of deaths expected in those cohorts with no vaccination. Numbers of persons vaccinated were based on 2011 GAVI Strategic Demand Forecasts with projected dates of vaccine introductions, vaccination coverage, and target population size in each country. By 2020, nearly all GAVI-supported countries with endemic disease are projected to have introduced hepatitis B, Hib, pneumococcal, rotavirus, rubella, yellow fever, N. meningitidis serogroup A, and Japanese encephalitis-containing vaccines; 55 (75 percent) countries are projected to have introduced human papillomavirus vaccine. Projected use of these vaccines during 2011-2020 is expected to avert an estimated 9.9 million deaths. Routine and supplementary immunization activities with measles vaccine are expected to avert an additional 13.4 million deaths. Estimated numbers of deaths averted per 1000 persons vaccinated were highest for first-dose measles (16.5), human papillomavirus (15.1), and hepatitis B (8.3) vaccination. Approximately 52 percent of the expected deaths averted will be in Africa, 27 percent in Southeast Asia, and 13 percent in the Eastern Mediterranean. Vaccination of persons during 2011-2020 in 73 GAVI-eligible countries is expected to have substantial public health impact, particularly in Africa and Southeast Asia, two regions with high mortality. The actual impact of vaccination in these countries may be higher than our estimates because several widely used antigens were not included in the analysis. The quality of our estimates is limited by lack of data on underlying disease burden and vaccine effectiveness against fatal disease outcomes in developing countries. We plan to update the estimates annually to reflect updated demand forecasts, to refine model assumptions based on results of new information, and to extend the analysis to include morbidity and economic benefits. Copyright © 2013. Published by Elsevier Ltd.