Thesis (Ph.D.) - Indiana University, School of Public Health/University Graduate School, 2019India has introduced several vaccines and intensified decentralized vaccine delivery during the Decade of Vaccines (2010-2020). Alongside, there is high-level consensus that community engagement (CE) improves vaccination uptake and reduces burden of vaccine preventable diseases. Despite progresses, existing evidence showcase lack of appropriate CE resulting in communities’ resistance and backlashes leading to lower vaccination uptake. In addition, there is no evidence regarding ‘what’ vaccine decision-makers think regarding CE, and ‘if’ communities are engaged beyond individual decisions to vaccinate themselves and their children. This is problematic, because assuming a shared understanding of CE will only lead to erroneous assumptions about its value, or lack thereof. This study uses three-stage concurrent and sequential qualitative methods to examine decision-makers’ conceptualization of CE, and barriers and enablers to implement CE during the Decade of Vaccines. Twenty-five elite interviews among national-level vaccine decision-makers was triangulated with content analysis of 24 vaccine policy documents and researcher field notes. Participant follow-up meetings was convened from December 2018 to January 2019. Findings were reported using Social Ecological Model (SEM). Decision-makers conceptualized communities variously: vaccine-eligible children, their parents, local-level vaccination influencers like health-workers, religious leaders, NGOs and vii CBOs. The study identified broad spectrum of CE, expanding from the utilitarian-empowerment dichotomy. CE evolution ranged from house-to-house polio delivery to tailored interventions and information dissemination for vaccination among vaccine-eligible and resistant communities. CE barriers exceeded enablers at all SEM levels. Policy-level enablers included political will promoting social mobilization, whereas lack of a CE strategy was barrier. At organizational level, cascade training of health-workers was considered a facilitator, whereas intrinsic power relations within communities, and paternalistic attitude of authorities with communities were inhibitors. Partnerships with local organizations though acknowledged, their lack of institutionalization was a CE barrier at the organizational-level. At interpersonal-level, social behavioral change communication and social-media messaging influenced communities’ vaccination decisions. However, impromptu rumor management tactics and lack of strategies to replicate CE best practices hindered engagement. Participants recommended developing operational definition of CE in the vaccine arena. Future studies should codify CE and its process-indicators in policy documents. Studies should map CE within intersectionalities to tailor strategies such that efficacious vaccines become effective vaccinations among communities.