This chapter of the book, India and Southeast Asia in a Changing World,  examines how India’s Act East Policy (AEP), initially implemented from 2014–2019 to strengthen ties with Southeast Asia, adapted in response to the COVID-19 pandemic through the emergence of vaccine diplomacy. With Southeast Asian nations identified as key partners, the chapter explores how vaccine diplomacy became a strategic tool for advancing AEP objectives during the global health crisis. It provides a detailed review structured in three parts: first, analyzing the strategic importance of Southeast Asia within India’s vaccine diplomacy efforts; second, outlining the specific modalities through which India implemented this approach; and third, assessing the impact of these efforts on the broader implementation and future trajectory of AEP in the region. This comprehensive analysis sheds light on how health diplomacy reshaped regional engagement during a critical period.