Impact of Covid-19 on Routine Immunization and Disease Surveillance in Delta State, Nigeria: A Mixed Methods Assessment of Service Disruptions and Recovery Patterns (2018–2022)

Background: The COVID-19 pandemic significantly disrupted routine immunization services globally, with low-resource settings like Nigeria particularly impacted due to long-standing health system weaknesses. Objectives: This study examined trends in immunization coverage, service delivery disruptions, facility ownership patterns, and the incidence of vaccine-preventable diseases (VPDs) in Delta State, Nigeria, from 2018 to 2022. Methods: A retrospective mixed-methods design was employed. Quantitative data were drawn from the Health Management Information System (HMIS), Integrated Disease Surveillance and Response (IDSR) reports, and facility records. Qualitative data were collected through key-informant interviews. Descriptive statistics were used to summarize trends, while Poisson regression assessed year-on-year differences in reported VPD cases. Thematic analysis was applied to explore operational and contextual challenges. Results: Immunization coverage declined from 78% in 2019 to 66% in 2022. Outreach sessions fell sharply in 2020 and showed only partial recovery. Urban LGAs with private-sector involvement recovered faster than rural areas relying on public services. Peaks in measles (31 cases) and hepatitis B (52 cases) occurred in 2020. Poisson regression indicated no statistically significant association between reporting year and overall VPD incidence (p > 0.05). Qualitative findings highlighted cold-chain limitations, workforce shortages, and community-level vaccine hesitancy as key barriers to service continuity. Conclusion: The pandemic exposed and deepened systemic weaknesses in Delta State’s immunization infrastructure. Strengthening rural outreach, enhancing private-sector collaboration, and investing in cold-chain systems are critical to restoring vaccine coverage and building resilience against future disruptions.