Missed opportunities for vaccination (MOV) reflect quality of immunization service. The objective of this study was to assess vaccination timeliness, prevalence, and characteristics of MOVs among children aged 0–23 months, as well as knowledge, attitude and practice of health workers towards immunization. An exit interview method was used to select caregivers and health personnel. Selection took place in 26 health facilities within 14 health areas in the Dshcang Health district. Data were collected using two face-to-face questionnaires adapted from the World Health Organization (WHO) tools. We conducted an evaluation of all free vaccines in the Expanded Programme on Immunisation (EPI). We studied timeliness, assessed MOV, and knowledge, behaviour and attitude of health workers on immunization. Basic statistical tests were used to study the association between MOV and socio demographic characteristics. A total of 363 children aged 0 to 23 months were surveyed. A total of 88 (91.66%) of health personnel agreed to participate in our study. A total of 298 (82.1%) children had vaccination cards with dates, leading to 18% not completely vaccinated. Vaccination timeliness ranged from 20% to 77%. Overall MOV estimated was 23.83%, range from 0% to 16.4% among all vaccines. Among health workers, 70.45% (62/88) had insufficient knowledge on vaccination, 73.86% assessed the vaccination status of children during any routine visit and 74% ask parents to bring the child’s vaccination record to any health facility visit. The study highlighted presence of MOV among children. Strategies for remedying this includes strengthening parents’ knowledge, organizing refresher courses for health workers on vaccination, and systematically assessing children’s vaccination status.