Using geospatial models to map zero-dose children: factors associated with zero-dose vaccination status before and after a mass measles and rubella vaccination campaign in Southern province, Zambia

Abstract

IntroductionDespite gains in global coverage of childhood vaccines, many children remain undervaccinated. Although mass vaccination campaigns are commonly conducted to reach these children their effectiveness is unclear. We evaluated the effectiveness of a mass vaccination campaign in reaching zero-dose children.MethodsWe conducted a prospective study in 10 health centre catchment areas in Southern province, Zambia in November 2020. About 2 months before a national mass measles and rubella vaccination campaign conducted by the Ministry of Health, we used aerial satellite maps to identify built structures. These structures were visited and diphtheria-tetanus-pertussis (DTP) and measles zero-dose children were identified (children who had not received any DTP or measles-containing vaccines, respectively). After the campaign, households where measles zero-dose children were previously identified were targeted for mop-up vaccination and to assess if these children were vaccinated during the campaign. A Bayesian geospatial model was used to identify factors associated with zero-dose status and measles zero-dose children being reached during the campaign. We also produced fine-scale zero-dose prevalence maps and identified optimal locations for additional vaccination sites.ResultsBefore the vaccination campaign, 17.3% of children under 9 months were DTP zero-dose and 4.3% of children 9–60 months were measles zero-dose. Of the 461 measles zero-dose children identified before the vaccination campaign, 338 (73.3%) were vaccinated during the campaign and 118 (25.6%) were reached by a targeted mop-up activity. The presence of other children in the household, younger age, greater travel time to health facilities and living between health facility catchment areas were associated with zero-dose status. Mapping zero-dose prevalence revealed substantial heterogeneity within and between catchment areas. Several potential locations were identified for additional vaccination sites.ConclusionFine-scale variation in zero-dose prevalence and the impact of accessibility to healthcare facilities on vaccination coverage were identified. Geospatial modelling can aid targeted vaccination activities.

Correlates of Zero-Dose Vaccination Status among Children Aged 12–59 Months in Sub-Saharan Africa: A Multilevel Analysis of Individual and Contextual Factors

“…To the best of our knowledge, this is the first study to estimate the prevalence of children with zero-dose vaccination status, using nationally representative surveys of 33 countries in SSA. Our study mirrors the result of Bosch-Capblanch et al, who reported prevalence of 9.9% of zero-dose children aged 12–59 months in LMICs [ 25 ]. Therefore, the current study underscores the need to increase efforts to move the zero-dose status children to fully vaccinated status in SSA.…”

“…The majority of these unvaccinated children live in the inner communities of SSA countries that are difficult to access by healthcare workers [ 53 ]. In 2020, as a result of the COVID-19 pandemic, most LMICs faced several challenges in basic healthcare services without exceptions to childhood immunization [ 25 ]. Therefore, the number of zero-dose children is expected to double as a result of the COVID-19 pandemic [ 54 ].…”

“…Children with zero-dose vaccination status are at increased risk for infections with vaccine preventable diseases (VPDs) such as measles, polio, and pneumonia, during the first 5 years of life [ 23 ]. They are also part of the world’s most vulnerable population, more likely to suffer from disability and mortality that could easily be prevented through immunization [ 24 , 25 , 26 ]. These children are predominantly less privileged, live in rural households, and raised by mothers with little or no education, indicating disparity within countries [ 27 , 28 , 29 ].…”

“…A comprehensive multinational study with primary focus in SSA is needed to fill these gaps. Arambepola et al, reported that incomplete knowledge on factors influencing zero-dose children in SSA needs to be properly investigated [ 25 ]. Given the growing concern of changing the status of children from zero-dose to fully vaccinated is yet to be addressed, more studies are needed to identify factors affecting zero-dose children [ 24 , 31 ].…”

Children of more empowered women are less likely to be left without vaccination in low- and middle-income countries: A global analysis of 50 DHS surveys

“…Thus, the current level of empowerment may have been different relative to when vaccination was due. Although we have chosen a zero-dose definition used by the UNICEF and the WHO (those who received no doses of DTP [ 21 , 23 ]) and other studies [ 37 , 38 ], it is not a complete zero-dose. The idea behind the operationalization of zero-dose taking into account only DPT is because having no doses of DPT is a good proxy of poor access to routine immunization and other health services.…”