Geographical and time trends of measles incidence and measles vaccination coverage and their correlation in Nigeria.

Nigeria has one of the highest measles burdens in the world. While measles-containing vaccine is proven to be effective in reducing measles cases, empirical studies on the correlation between measles incidence and measles vaccine coverage in Nigeria has been limited. The aim of this study was to conduct a detailed analysis on measles incidence, measles vaccine coverage, and their correlation between 2012 and 2021. A retrospective observational study was conducted based on the Integrated Disease Surveillance and Response (IDSR) data for the measles incidence in each Nigerian state over time, District Health Information System, V.2 (DHIS2) and Nigeria Demographic and Health Survey (DHS) for the coverage of the first dose of measles containing vaccine (MCV1) over time (2012-2021). We observed the trend of measles incidence and measles vaccine coverage, as well as their correlation. Out of the study period from 2012 to 2021, we found that the majority of measles outbreaks occurred in the northeastern states in recent years after 2019, especially in Borno state, where Boko Haram insurgency has negatively impacted health service delivery, including routine vaccination. We observed a significant negative correlation between measles incidence and measles vaccine coverage across Nigerian states. However, there was no sudden drop in measles vaccine coverage before the recent outbreak in Borno state in 2019, which could be due to various factors other than the overall vaccine coverage.