Trends in measles incidence and measles vaccination coverage in Nigeria, 2008-2018

How did the introduction of the measles-containing vaccine second dose (MCV2) affect measles vaccine uptake? - evidence from Nigeria

Nigeria has the highest burden of measles worldwide, as measles vaccine uptake remains low. Recently, the second dose of the measles-containing vaccine (MCV2) was introduced as part of the routine immunization (RI) program, and this study examined how it changed the uptake of the measles vaccine and the factors associated with vaccination behavior. The Nigeria Multiple Indicator Cluster Survey (MICS) 2021 was used to compare measles vaccination uptake as well as factors associated with vaccination uptake between children before MCV2 introduction (cohort 1) and after the introduction (cohort 2). The overall rate of measles vaccine uptake was higher among cohort 1 (64%-95%) than among cohort 2 (56%-92%) in all zones because of younger age among cohort 2. The dropout from the first to second measles vaccines was similar between the cohorts (around 24%). Higher maternal education levels and higher household wealth levels were both correlated with the vaccine uptake or both cohorts but a positive correlation between the dropout and mother's education level was observed only among cohort 2, especially in the North West and South West zones. The positive correlation between the dropout and mother's education level among cohort 2 indicates that the introduction of MCV2 as part of RI might have helped to narrow the disparity in measles vaccine uptake in North West and South West zones. Further study is required to investigate strategies employed to reduce the disparity in these zones to apply nationwide.

Geospatial Analyses of Recent Household Surveys to Assess Changes in the Distribution of Zero-Dose Children and Their Associated Factors before and during the COVID-19 Pandemic in Nigeria

The persistence of geographic inequities in vaccination coverage often evidences the presence of zero-dose and missed communities and their vulnerabilities to vaccine-preventable diseases. These inequities were exacerbated in many places during the coronavirus disease 2019 (COVID-19) pandemic, due to severe disruptions to vaccination services. Understanding changes in zero-dose prevalence and its associated risk factors in the context of the COVID-19 pandemic is, therefore, critical to designing effective strategies to reach vulnerable populations. Using data from nationally representative household surveys conducted before the COVID-19 pandemic, in 2018, and during the pandemic, in 2021, in Nigeria, we fitted Bayesian geostatistical models to map the distribution of three vaccination coverage indicators: receipt of the first dose of diphtheria-tetanus-pertussis-containing vaccine (DTP1), the first dose of measles-containing vaccine (MCV1), and any of the four basic vaccines (bacilli Calmette-Guerin (BCG), oral polio vaccine (OPV0), DTP1, and MCV1), and the corresponding zero-dose estimates independently at a 1 × 1 km resolution and the district level during both time periods. We also explored changes in the factors associated with non-vaccination at the national and regional levels using multilevel logistic regression models. Our results revealed no increases in zero-dose prevalence due to the pandemic at the national level, although considerable increases were observed in a few districts. We found substantial subnational heterogeneities in vaccination coverage and zero-dose prevalence both before and during the pandemic, showing broadly similar patterns in both time periods. Areas with relatively higher zero-dose prevalence occurred mostly in the north and a few places in the south in both time periods. We also found consistent areas of low coverage and high zero-dose prevalence using all three zero-dose indicators, revealing the areas in greatest need. At the national level, risk factors related to socioeconomic/demographic status (e.g., maternal education), maternal access to and utilization of health services, and remoteness were strongly associated with the odds of being zero dose in both time periods, while those related to communication were mostly relevant before the pandemic. These associations were also supported at the regional level, but we additionally identified risk factors specific to zero-dose children in each region; for example, communication and cross-border migration in the northwest. Our findings can help guide tailored strategies to reduce zero-dose prevalence and boost coverage levels in Nigeria.

Mapping the distribution of zero-dose children to assess the performance of vaccine delivery strategies and their relationships with measles incidence in Nigeria

Geographically precise identification and targeting of populations at risk of vaccine-preventable diseases has gained renewed attention within the global health community over the last few years. District level estimates of vaccination coverage and corresponding zero-dose prevalence constitute a potentially useful evidence base to evaluate the performance of vaccination strategies. These estimates are also valuable for identifying missed communities, hence enabling targeted interventions and better resource allocation. Here, we fit Bayesian geostatistical models to map the routine coverage of the first doses of diphtheria-tetanus-pertussis vaccine (DTP1) and measles-containing vaccine (MCV1) and corresponding zero-dose estimates in Nigeria at 1x1 km resolution and the district level using geospatial data sets. We also map MCV1 coverage before and after the 2019 measles vaccination campaign in the northern states to further explore variations in routine vaccine coverage and to evaluate the effectiveness of both routine immunization (RI) and campaigns in reaching zero-dose children. Additionally, we map the spatial distributions of reported measles cases during 2018 to 2020 and explore their relationships with MCV zero-dose prevalence to highlight the public health implications of varying performance of vaccination strategies across the country. Our analysis revealed strong similarities between the spatial distributions of DTP and MCV zero dose prevalence, with districts with the highest prevalence concentrated mostly in the northwest and the northeast, but also in other areas such as Lagos state and the Federal Capital Territory. Although the 2019 campaign reduced MCV zero-dose prevalence substantially in the north, pockets of vulnerabilities remained in areas that had among the highest prevalence prior to the campaign. Importantly, we found strong correlations between measles case counts and MCV RI zero-dose estimates, which provides a strong indication that measles incidence in the country is mostly affected by RI coverage. Our analyses reveal an urgent and highly significant need to strengthen the country's RI program as a longer-term measure for disease control, whilst ensuring effective campaigns in the short term.

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.

Using Household Surveys to Assess Missed Opportunities for Simultaneous Vaccination: Longitudinal Examples from Colombia and Nigeria

One important strategy to increase vaccination coverage is to minimize missed opportunities for vaccination. Missed opportunities for simultaneous vaccination (MOSV) occur when a child receives one or more vaccines but not all those for which they are eligible at a given visit. Household surveys that record children’s vaccination dates can be used to quantify occurrence of MOSVs and their impact on achievable vaccination coverage. We recently automated some MOSV analyses in the World Health Organization’s freely available software: Vaccination Coverage Quality Indicators (VCQI) making it straightforward to study MOSVs for any Demographic & Health Survey (DHS), Multi-Indicator Cluster Survey (MICS), or Expanded Programme on Immunization (EPI) survey. This paper uses VCQI to analyze MOSVs for basic vaccine doses among children aged 12–23 months in four rounds of DHS in Colombia (1995, 2000, 2005, and 2010) and five rounds of DHS in Nigeria (1999, 2003, 2008, 2013, and 2018). Outcomes include percent of vaccination visits MOSVs occurred, percent of children who experienced MOSVs, percent of MOSVs that remained uncorrected (that is, the missed vaccine had still not been received at the time of the survey), and the distribution of time-to-correction for children who received the MOSV dose at a later visit.