Measles Epidemiology in the Amhara Regional State, Ethiopia (2019-2024): Trends, Distribution, and immunity Gaps

A study spanning 2019 to 2024 in the amhara Regional State of Ethiopia reveals critical insights into the epidemiology of measles. A total of 18,468 suspected cases were reported, with 9% (1,571 cases) confirmed via laboratory testing using IgM ELISA. while a significant proportion of cases were clinically compatible (61%) or epidemiologically linked (20%),diagnostic confirmation remains a challenge.

The highest measles burden was observed among children aged 5-14 years (49%), followed by those aged ≥15 years (26%), indicating immunity gaps extending beyond early childhood. Specific zones – Waghimra, Central Gondar, Oromo Special, and East Gojjam – experienced a disproportionately high number of cases, with seasonal peaks occurring in spring (March-May) and autumn (September-November). The crude incidence rate increased from 0.53 to 2.13 per 100,000 population, peaking in 2023, likely linked to disruptions in vaccination programs and healthcare access due to local conflicts.

Limited laboratory confirmation is attributed to restricted access to measles IgM ELISA test kits, logistical hurdles in sample transport to the region’s single testing facility, and its inaccessibility to remote areas – challenges mirroring those observed globally in low-resource settings.

Notably, the age distribution of cases in Amhara differs from the global pattern, where the majority of cases occur in children under five.The high proportion of cases in the 5-14 age group suggests waning immunity in previously immunized children or insufficient vaccine coverage in older cohorts. This trend is similar to that seen in the Democratic Republic of Congo, and may reflect historically low vaccine coverage leading to a build-up of susceptible individuals. Maintaining immunity is further elaborate by logistical challenges, inadequate health infrastructure, ongoing conflicts, and increased exposure risk among school-aged children.

The concentration of cases in Waghimra, Central Gondar, oromo Special, and East Gojjam zones may be linked to geographical inaccessibility and limited healthcare access due to challenging terrain and inadequate transportation.

Interestingly, a majority of confirmed cases occurred in individuals reported as vaccinated. This might potentially be due to the exclusion of cases with unknown vaccination status from the analysis, potentially skewing the data. Moreover, individuals who received only a single dose of the measles vaccine were more susceptible than those who received two or three doses, highlighting the importance of booster doses for sustained immunity.

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Measles Epidemiology in the Amhara Regional State

The highest measles IgM positivity rate was observed in 2019, while the lowest was recorded in 2022, a trend that is consistent with earlier evidence from global reports [78], immunization reviews in Africa [79], Sub-Saharan Africa countries [80], tanzania [81], and Nigeria [82] reports on measles epidemiology. The elevated positivity rate in 2019 might be attributed to low vaccination coverage,which has resulted in gaps in herd immunity and left a large population susceptible to infection after the COVID-19 pandemic. Additionally, this might be related to the global resurgence of measles reported in several countries, including Samoa, the Democratic Republic of the Congo (DRC) [83, 84], and Ukraine [85]. Conversely, the lower positivity rate observed in 2022 may be linked to improved measles vaccine coverage in the post-COVID-19 era, especially through catch-up immunization campaigns conducted after outbreak periods. The reduction in susceptible individuals may have also been influenced by the widespread COVID-19 vaccination efforts. furthermore, public health measures implemented for COVID-19 prevention, such as masking, social distancing, and restrictions on large gatherings including cultural and spiritual ceremonies may have temporarily suppressed measles transmission during this period.

Our spatial analysis revealed that the distribution of measles cases in the Amhara Regional State is not random. The spatial autocorrelation analysis indicated a clustered pattern, with certain woredas experiencing significantly higher concentrations of measles cases, while others had consistently low case numbers throughout the study period (2019-2024). This finding aligns with studies conducted in other regions, including Lusaka, Zambia in Africa [86], Greece [87], Germany [88], and Italy [89] in Europe, and China in Asia [90].

The hotspot analysis identified distinct hot spot areas in the distribution of measles cases across the Amhara Regional State. Additionally, the SaTScan statistical analysis detected significant cluster areas with high measles case reports during the study period. The most significant clusters were observed in clustering Woredas from Oromo Special zone in the year 2019, 2023; Waghimra zone in the year 2020, 2021, 2024; Central Gondar Zone in 2021, South Gondar zone in 2021, North Shoa zone in 2022 and 2023, and North Wollo zone in 2020. The evidence of significant clusters of measles cases in hot spot pockets in this study is also supported with earlier local evidence [91]. Similar to this study,in many African countries like Ghana [92],zambia [93],Tanzania [94] a significant clustering of measles cases in hotspot pockets has been reported.

The significant clustering of measles cases in these locations can be attributed to several factors. These clusters likely represent areas where measles vaccination coverage remains below the critical 95% threshold and a significant clustering of low measles vaccine coverage in Sub-Saharan countries [95], Ethiopia[[96,