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

Abstract

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 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.

Measles Vaccine Coverage and Disease Outbreaks: A Systematic Review of the Early Impact of COVID-19 in Low and Lower-Middle Income Countries

“…In a tertiary hospital setting in Pakistan, Rahman et al reported that the MCV1 and MCV2 vaccination rate was the single most affected antigen within the EPI schedule, with lowest recovery when comparing percentage change for COVID-19 interruption and early recovery with pre-COVID baseline vaccination rates (EPI vaccines −36.2% to −11.7%; MCV1 -40.9% to −17.8%; MCV2 -48.6% to −20.7%) [ 48 ]. Utazi et al [ 57 ] hypothesised that MCV1 and MCV2 showed a disproportionate reduction over other EPI vaccine antigens because they are administered later in life, as opposed to those given at birth (potentially with a healthcare provider present) or in the first few months of life. Contrarily, studies in Pakistan, Ghana and Sierra Leone identified a greater reduction in doses given at the start of the childhood schedule and attributed this as due to a reduction in births in hospitals [ 26 , 43 , 46 , 48 ].…”

“…Anxiety surrounding vaccination has also increased in response to misleading information spread on social media [ 70 ]. Increasing vaccine hesitancy was cited as a specific challenge for vaccination campaigns in multiple included studies [ 10 , 43 , 44 , 57 ].…”

“…[61] "2021 nationwide measles vaccination campaign postponed due to pandemic and global supply shortage." [57] "Overburdened health systems, depreciation in standard delivery of immunization services in regions of Zimbabwe." [63] "Reports for seven (23%) of 30 countries indicated challenges with vaccine supply" [21] Lockdowns 14 "Immunisation of new-borns were temporarily deferred in Bhutan during nationwide lockdown periods."…”

“…[48] "Ban on interstate movement reduced access to healthcare facilities." [57] "Reduction in immunisation clinics p < 0.0001. In April immunisation services were completely suspended."…”

“…[47] "Cancelled SIAs-SIA was planned in 2020 in the south, postponed due to COVID-19 pandemic." [57] Staff absences 10 "3% decline in the public health sector staffing level." [27] "Reduction in mean proportion of vaccinators attending work, with greater loss of female workers (13.7%, 95% CI: 12.9-14.5) compared to male vaccinators (6.3%, CI: 6.0-6.6)."…”