Introduction

Immunization is one of the most cost-effective interventions for the reduction of childhood morbidity and mortality. It is reported that immunization averts an estimated 2.5 million deaths every year from diphtheria, tetanus, pertussis (whooping cough), and measles (Global Vaccine Action Plan 2011-2020). Significant improvements in vaccination coverage have been made globally since 1980s due to substantial investment in childhood immunization services. However, in the past decade, progress has stalled, and routine vaccination coverage has declined in many countries. The global coverage of the first dose of a diphtheria-tetanus-pertussis-containing vaccine (DTP1) and the first dose of a measlescontaining vaccine (MCV1) fell from 90% and 86% in 2019 and further to 86% and 81% in 2021 [1]. Disruption to routine vaccination activities brought about by the COVID-19 pandemic further contributed to poor immunization performance in many countries [2].

Coverage of the DTP-containing vaccine is one of the main indicators for monitoring the performance of immunization programs because it is universally present in all national vaccination schedules for children under one year and requires three contacts with the healthcare system [3]. Immunization programs use coverage of DTP1 as a proxy for zero-dose children ( i.e., those who have not received a single shot of vaccines). Nearly half of these children live in urban areas, remote communities, and conflict-affected setting [4]. In 2020, it was estimated that about 12.4 million children mostly in low-income countries were zero-dose, leaving them exposed to the world’s most devastating vaccine-preventable diseases [5]. In 2021, according to UNICEF, 18 million children were zero-dose and 25 million were under-vaccinated (having not received all required vaccines) [1].

Poor coverage of immunization exposes children to deadly vaccine-preventable diseases. The sub-Saharan Africa region has the highest mortality rate for children under five worldwide, accounting for 52% of all deaths in this age group [6]. One in 13 children in this region died before turning five in 2018, according to the region’s average under-five mortality rate of 78 deaths per 1,000 live births. This ratio is 16 times greater than the highincome country average of 1 in 199 children. The majority of these fatalities can be avoided with the provision of low-cost, interventions including vaccination, hygienic drinking water, proper nourishment, and appropriate care from qualified health professionals [6].

Tanzania, like many other countries in Sub-Saharan Africa, has experienced rapid urbanization since the 1960s. Several studies have shown that the urban population increased from 5% in 1967 to 23% in 2002 (URT, 2002) and further to 27% in 2012 (URT, 2012). It is projected that the urban population will surpass 20 million by 2030 [7]. Urbanization has been accelerated by rural-urban migration mostly in search of employment opportunities, natural population growth, and expansion of urban administrative boundaries (URT 2013, p.63). Rapid urbanization is surpassing the public sector’s ability to provide infrastructures to support the provision of basic social services including health. Rapid urbanization has increased the number of people living in slums and peri-urban poor communities with limited access to immunization services [8] These urban areas with low vaccination coverage have a high potential for transmission and outbreaks of vaccine-preventable diseases.

Reaching zero-dose children is a global, and national agenda in Tanzania. The Gavi Board approved a new five-year strategy (‘Gavi 5.0’) with a vision to ‘leave no one behind with immunization’ and a mission to save lives and protect people’s health by increasing equitable access and sustainable use of vaccines [9]. The new UNICEF Immunization Roadmap 2018-2030 has also placed equity in immunization as one of its key agendas. The roadmap has earmarked communities living in remote rural areas, urban slums, and conflict-affected/insecure settings as the most at-risk population groups that need urgent action [4]. WHOs Immunization Agenda 2030 also focus on leaving no one behind with immunization. The Tanzanian National Immunization Strategy (NIS-20212025) also has a focus on reaching zero-dose children. Within the GAVI 5.0, UNICEF Roadmap 2018-2030, the WHOs Immunization Agenda 2030, and NIS strategies, the zero-dose focus is developed, operationalized, and positioned for action. The idea of reaching zero-dose children has been taken forward by CHAI in Tanzania to reflect on outstanding questions regarding urban immunization and zero-dose children, particularly on how to define, target, and implement strategies, including identifying risks that need to be considered and mitigated. Therefore this implementation study aimed at improving urban immunization coverage in Dar es Salaam city by reducing the number of zero-dose children.

The study determined the immunization performance in terms of coverage, and factors behind poor performance and used the evidence gathered to redesign strategies to reach the zero-dose children.

Methodology

Study Setting

Dar es Salaam is the business capital of Tanzania. It is subdivided into five districts namely Ilala, Kinondoni, Temeke, Ubungo, and Kigamboni (Map 1). According to the 2022 census, Dar es Salaam has a population of about 5.3 million people, and a population density of more than 3100 people per km2, thus making it the most densely populated region in Tanzania. Originally, Dar es Salaam was ethnically inhabited by the Zaramo, however, the immigration of other tribes has made the region to be culturally diverse. More than three-quarters of the residents live in informal settlements and are mostly involved in business [10].

Map 1: Dar es Salaam region and its five districts

Identification of zero-dose children

We performed a desk review of routine immunization data for Dar es Salaam region to assess immunization performance in the five districts in terms of coverage and number of zero-dose children. We also assessed challenges of service delivery and coverage trends for Bacille Calmette-Guérin (BCG), the first dose of diphtheria-tetanus-pertussis-containing vaccine (DTP1), and DTP3 for the years 2020 and the first quarter of 2021. Dar es Salaam has 783 health facilities in total, but only 318 (41%) offer vaccination services. Kigamboni has the highest proportion of health facilities offering vaccination services at 80%, followed by Temeke (71%), Ubungo (42%), Ilala (37%), and Kinondoni (24%).

With regards to the performance of the immunization program, the aggregate coverage data at the regional level for BCG, DTP1, and DTP3 for the year 2020 was high and a similar trend was observed in the first quarter of 2021 (National Immunization data). The data when disaggregated by districts showed that all three antigens had coverage of above 100% except in Ilala with DTP1 coverage of 93% and DTP3 of 90%, and Ubungo with a BCG coverage of 88%. DTP1 coverage—the proxy for zero-dose children was high, necessitating another way of examining the data to understand the true prevalence of zero-dose children. Therefore, instead of using the estimated target population for DTP1, we used the number of children that were vaccinated with BCG. These two vaccines are both given at birth, hence coverage is supposed to be the same. However, we found that many children who received BCG did not receive the corresponding DTP1 vaccine in Ilala and Kigamboni districts as shown in Table 1. Therefore, the implementation study was focused on these two districts with the highest number of zero-dose children.

Table 1:Immunization performance in the five districts of Dar es Salaam region in 2020

SI-Surviving infants, IMR-Infant mortality rate, BCG- Bacille Calmette-Guérin, DTP- diphtheria-tetanus-pertussis-containing vaccine.

Site selection and health facilities mapping

Facilities with a high number of zero-dose and under-vaccinated children in the two districts were mapped based on the immunization performance data. QGIS, a free and open-source geographic information system was used to visualize coverage as shown in Figures 1 and 2. In Ilala and Kigamboni districts, coverage for DTP1 and DTP3, was low in the outskirts of the district, particularly in areas that have no nearby health facilities.

Figure 1:The year 2020 coverage in Ilala (A) DTP1 and (B) DTP3

Figure 2: The year 2020 in Kigamboni (A) DTP1 and (B) DTP3 Similarly, we mapped areas with high zero-dose children (DTP1) as of December 2020. As shown in Figure 3, the high number of zero-dose children in Ilala was concentrated in the city center despite the high concentration of vaccination health facilities. In addition, in areas of new settlements and where the network of vaccinating health facilities is dispersed there are as well indications of unvaccinated children. In Kigamboni it was the opposite, zero-dose children were more in areas with sparse distribution of health facilities.

Figure 3: Zero-dose children in Ilala (A) and Kigamboni (B).

Developmentof an intervention package

To enhance urban immunization and reduce zero-dose children in the city of Dar es Salaam, we revised interventions and tactics being used in the region. To gather information about immunization practices and challenges faced by health facilities and parents/guardians of the children, we conducted field visits to 15 high-volume health facilities, three from each of the five districts of Dar es Salaam region. We conducted interviews with healthcare workers and parents and/or guardians. We included all five districts to get in-depth information to facilitate the formulation of a comprehensive intervention package.

We also conducted meetings with officers from the National Immunization and Vaccine Development Program (IVD), and the Regional and Council Health Management Teams (RHMT/CHMT) from all five districts to come up with best practices, challenges, and strategies to ensure coverage of zero-dose children. The top-performing healthcare facilities from each council discussed their high coverage strategy, which included extensive outreach, mobile clinics, and data-driven decision-making. Low-performing healthcare facilities posed problems such as a scarcity of employees, stockouts of vaccines and supplies, and staff attrition.

Based on these discussions and learnings from the interviews with the healthcare workers, parents/guardians of the children, regional and district health management teams, and IVD officials, we redesigned intervention strategies that were implemented from February to May 2022 in the ten health facilities. The redesigned intervention package targeted to: 

• Expand vaccination services to weekends i.e., Saturdays. This aimed to enable parents/caregivers who don’t find time during the weekdays to bring their children for vaccination on the weekend.
• Engage the corresponding community health workers within the catchment area (i.e. Community Health Workers in the surrounding areas were involved in making follow-ups of under-vaccinated children and identification of zero-dose children, the CHWs often knew each family member by name, which children still needed to be vaccinated, and gained the trust required to complete vaccinations.).
• Increase the number of outreach posts in new emerging settlements, with healthcare workers assigned to visit each street at least twice a week.
• Increase the number of social mobilizers to conduct public announcements in these new settlements to inform parents/caregivers of expanded services on Saturdays.

Implementation of the intervention package

Based on desk review and mapping, we selected ten health facilities that were documented to have the largest number of zerodose children based on data extracted from the immunization registers. The comprehensive intervention package that was designed was implemented in these ten health facilities. We held orientation sessions with healthcare workers and community health workers from each of these health facilities that were chosen to learn how immunization sessions were currently run and to come up with ideas for reaching zero-dose children. Similar sensitization meetings were held with community leaders in the catchment areas.

Data collection tools, and analysis

During the implementation phase, numerous instruments for the data collection on under and zero-dose children reached were created. The organization of the data gathered in each geography was spearheaded by facility health professionals, who then reported the monthly data to CHAI. Data collected were compiled and analyzed and findings were shared with facilities and also by regional and council Health Management teams quarterly. Final results were also shared with the Ministry of Health (the IVD program) and with other immunization partners.

Results

From the detailed review of documents and data analysis, we identified 1,266 zero-dose children (as of December 2021) from the ten health facilities in Ilala and Kigamboni districts. Through redesigned intervention package, a total of 651, which is equivalent to 51% of the identified zero-dose children were reached by community health workers and brought back to the health facilities for vaccination. We used the same opportunity to also reach 1,209 under-vaccinated children for OPV3, 912 for DTP3, and 295 for MR2 (Table 2).

Table 2:Zero-dose and under-vaccinated children reached in ten selected facilities

Effectiveness of strategies used

Vaccination during the weekend i.e., Saturday

During the four months of implementation in the ten selected health facilities, we also introduced vaccination sessions on Saturdays, as most parents in urban areas were busy during weekdays. Through this approach, a total of 1,105 children were vaccinated (Table 3).

Table 3:Children reintegrated into health facilities during Saturday vaccination sessions.

Vaccinations in newly established outreach posts in new emerging settlements

Moreover, as Dar es Salaam city is expanding and there are more emerging settlements we established new outreach posts in new emerging settlements outside the city. Through this approach, a total of 880 children were reintegrated into the health facilities for vaccination and received the appropriate vaccination (Table 4).

Table 4:Children vaccinated on newly established outreach posts in new emerging settlements.

The work also revealed low coverage for the measles-rubella vaccine second dose (MR-2) for children under one. These pockets of low coverage create a risk for the reintroduction of vaccine-preventable diseases that have been eradicated, eliminated, or are under epidemiological control. While this intervention revealed children missing DTP1 in two specific municipal councils (Ilala and Kigamboni), there remains a knowledge gap regarding the number of zero-dose in the whole region and countrywide.

Tracking of zero dose and under-vaccinated children

Community health workers serving the catchment areas surrounding the ten health facilities played a big role in tracking the zerodose and under-vaccinated children in the two study districts. Before this, community health workers were trained on the methods of tracking zero-dose children and on the use of tools to record all eligible children found. They were also given a list of 2,752 children found in the registers who never returned for their subsequent vaccine doses. Apart from these, community health workers were also able to come up with a list of 1,705 children eligible that were not listed in facility registers (Figure 5). These are the ones from new emerging settlements in Ilala and Kigmaboni.

Figure 5:Tracking of eligible children through registers and CHWs.