Rendahnya cakupan imunisasi dasar lengkap (IDL) di wilayah perbatasan berpulau, khususnya Kabupaten Kepulauan Sangihe dan Talaud, mencerminkan tantangan geografis, logistik, sosial-budaya, serta ketidakstabilan tata kelola yang tidak terakomodasi oleh kebijakan nasional yang bersifat seragam. Penelitian ini bertujuan mengembangkan model kebijakan adaptif IDL berbasis konteks kepulauan untuk memperkuat respons sistem imunisasi daerah. Desain penelitian menggunakan mixed-method sequential explanatory, diawali survei kuantitatif terhadap 101 ibu balita untuk menguji hubungan determinan geografis, akses layanan, pengetahuan, sikap, dan persepsi kebijakan terhadap status IDL. Tahap kualitatif melibatkan 32 informan kunci (pemerintah daerah, puskesmas, tokoh adat/agama, kader, dan ibu balita) melalui wawancara mendalam untuk mengeksplorasi faktor-faktor struktural, sosial budaya, serta dinamika tata kelola. Hasil penelitian menunjukkan bahwa tidak adanya signifikansi statistik pada beberapa variabel utama menandakan dominasi hambatan struktural, khususnya ketidakpastian geografis, logistik rantai dingin, dan koordinasi lintas sektor. Analisis tematik mempertegas bahwa kebijakan nasional belum adaptif terhadap arsitektur archipelagic governance. Penelitian ini menghasilkan Model Kebijakan Adaptif KAIL–KAIT–POLA 2.0, yang menekankan fleksibilitas operasional, komunikasi lintas-aktor, dan tata kelola kolaboratif untuk meningkatkan stabilitas cakupan IDL. Rekomendasi mencakup penyusunan SOP adaptif kepulauan, penguatan transportasi vaksin, integrasi tokoh adat, dan perluasan ruang keputusan daerah.

Coverage of complete basic immunization (CBI) in Indonesia’s archipelagic border regions remains persistently low, particularly in the Sangihe and Talaud Islands, where geographical fragmentation, logistical uncertainty, and socio-cultural dynamics hinder effective policy implementation. This study aims to develop an adaptive CBI policy model tailored to archipelagic border contexts. A mixed-method sequential explanatory design was employed, beginning with a quantitative survey of 101 mothers of under five children to examine associations between geographic access, service availability, knowledge, attitudes, and policy perception with CBI status. The qualitative phase involved 32 key informants (district officials, health managers, puskesmas staff, community and religious leaders, and mothers) through in-depth interviews to explore structural barriers, cultural determinants, and governance dynamics. Quantitative results revealed limited statistical significance across several determinants, indicating predominant structural constraints, including unstable maritime transport, cold-chain vulnerabilities, and rigid top-down policy mechanisms. The qualitative synthesis demonstrated misalignment between national immunization policy and the realities of archipelagic governance, where uncertainty is systemic and requires situational adaptation. The study formulates the KAIL–KAIT–POLA 2.0 Adaptive Policy Model, emphasizing flexible operational pathways, strengthened cross-actor communication, and collaborative governance to stabilize CBI coverage. Recommendations include developing adaptive SOPs for island settings, improving vaccine logistics, formalizing engagement of local leaders, and expanding local decision space. Keywords: complete basic immunization; adaptive policy; archipelagic governance; border island