To develop effective private donation campaigns that support vaccine distribution in low- and middle-income countries (LMICs), one must understand donors' willingness to give, response to stimuli, and preferences for program management. We use a contingent valuation method to estimate United States citizens' willingness to give to nongovernmental COVID-19 immunization programs in LMICs during the emergency phase of the pandemic. Using split-sample treatments, we evaluate the impact of the immunization program administrator (generic NGO or COVAX) and the role of priming communications on inequality in income and vaccination rates between the US and recipient countries. Results show that the median American would donate $42 towards global immunization programs. Preferences for program management and responses to priming communications are heterogeneous across political affiliations, after controlling for altruistic motives, experiences with COVID, giving behaviors, and sociodemographic characteristics. Specifically, Democrats and Independents are more likely to donate to the COVAX-administered fund, and more responsive to priming statements regarding vaccine-gaps. Policy implications are discussed.