OBJECTIVES: : Rotavirus is the most common cause of severe diarrhoea worldwide. This study was designed to evaluate the cost-effectiveness of rotavirus immunization in Vietnam taking into account herd immunity and patterns of breastfeeding. The affordability of implementing universal rotavirus immunization was assessed based on both GAVI-subsidized and market vaccine prices for the next 5 years from the perspective of the Vietnamese healthcare system. METHODS:  An age-structured birth cohort model for Vietnam was developed to compare two strategies of no vaccination and universal rotavirus vaccination in 2011. A lifetime time horizon was used with monthly time cycles for those under one year and annually thereafter. The analysis was performed under three breastfeeding scenarios: 1) 100% exclusive breastfeeding for children under 6 months; 2) 100% partial breastfeeding, and 3) 100% no breastfeeding. Herd immunity was explored in all scenarios. Monte Carlo simulations were used to examine the acceptability and affordability of the immunization strategy. RESULTS: Rotavirus immunization would effectively reduce severe cases of rotavirus during the first 5 years of life. Herd immunity makes rotavirus vaccination a cost-saving strategy under the GAVI-subsidized vaccine price in the case of partial breastfeeding and a cost-effective strategy in all breastfeeding scenarios under the market vaccine price. Affordability results showed that at the GAVI-subsidized vaccine price, rotavirus vaccination is affordable. CONCLUSIONS: This is the first study in developing countries considering herd immunity under rotavirus vaccination. If the indirect effect were considered, vaccination would become a cost-saving strategy. Given the high mortality rate of diarrhea in children under-five-years of age, our findings show rotavirus immunization to be an effective and “must-do” prevention strategy. Vaccination, however, only becomes affordable if Vietnam receives GAVI’s financial support. In the next five years, Vietnam will need financial support from international organizations to implement rotavirus vaccination.