Spatiotemporal Patterns of Measles Outbreaks in Rivers State, Nigeria (2020-2022)

<i>Background:</i> Measles remains a leading cause of child mortality globally despite an effective vaccine. Nigeria has persistent measles transmission due to suboptimal immunization coverage (around 54% for first dose)]. The study analyzed measles surveillance data of Rivers State from 2020-2022 to identify spatiotemporal clusters and outbreak characteristics by Local Government Area (LGA) and age group. <i>Methods:</i> A retrospective cross-sectional study conducted on measles case-based surveillance data for Rivers State from January 2020 to December 2022. Cases were aggregated by month, LGA, and age. Measles outbreak was defined as the number of laboratory-confirmed cases ≥3 in an LGA within 4 weeks Descriptive statistics summarized case counts by time, place, and age. Chi-square tests assessed associations between categorical variables (e.g. age group verses LGA, year verses age distribution). An epidemic curve and bar charts were used to visualize temporal trends and the distribution of cases by LGA and age group. <i>Results:</i> A total of 761 measles cases were reported in Rivers State from 2020-2022 (200 in 2020; 229 in 2021; 332 in 2022). The epidemic curve showed a peak of 70 cases in February 2020, a decline, a resurgence in mid-2021, and a larger outbreak in early 2022 (peak 61 cases in February 2022). Transmission persisted year-round at lower levels between these outbreaks. Spatial distribution of Cases occurred in all 23 LGAs, but 10 LGAs (led by Obio/Akpor and Port Harcourt) accounted for ~60% of cases. The age distribution of Cases ranged from infants to 79 years (median ~6 years, IQR 2-16). Children <5 years comprised 41% of cases, and 25% were aged ≥15 years. children (1-4 years) and adults also contributed substantial proportions, indicating gaps in historical vaccination coverage. <i>Conclusion:</i> Rivers State experienced recurrent measles outbreaks in 2020-2022 with clear spatiotemporal clustering. The pattern suggests a two-year cycle of major outbreaks, with an early 2020 peak, a smaller mid-2021 wave, and a large 2022 outbreak. All LGAs were affected, but the burden was more in certain urban centers and varied over time. Gaps in immunity were evident in both young children and older age groups, reflecting inadequate vaccination coverage.