**1. Background**

The most dramatic declines in routine immunization coverage in the last 30 years occurred in part due to the COVID-19 pandemic. There were approximately 25 million un-vaccinated or under-vaccinated children in 2021, out of which 18 million were zero-dose, based on the proxy indicator of the number of children who did not receive the first dose

**Citation:** Dadari, I.; Belt, R.V.; Iyengar, A.; Ray, A.; Hossain, I.; Ali, D.; Danielsson, N.; Sodha, S.V.; The Global Urban Immunization Working Group. Achieving the IA2030 Coverage and Equity Goals through a Renewed Focus on Urban Immunization. *Vaccines* **2023**, *11*, 809. https://doi.org/10.3390/ vaccines11040809

Academic Editor: Davide Gori

Received: 25 February 2023 Revised: 24 March 2023 Accepted: 3 April 2023 Published: 6 April 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

of a diphtheria-tetanus-pertussis-(DPT) containing vaccine [1]. This drop in coverage has resulted in an increase in the number of zero-dose children globally, from 13 million in 2019 to 18 million in 2021 (approximately 40% more zero-dose children) [2].

A greater focus on strategies to reach un- and under-vaccinated children in urban, rural, and conflict settings is encouraged by the Equity Reference Group on Immunization (ERG), as these populations are facing acute inequities [1]. Due to rapid global urbanization, the world's population is at least 56% urbanized as of 2020 and expected to reach 70% by 2050 [2]. This fast urbanization is not devoid of complications, especially in low- and middle-income countries (LMICs) where the numbers of large informal settlements and urban-poor populations are growing, resulting in huge inequalities in access to basic primary healthcare services, including immunization [3], as such a shift in the distribution of zero-dose and under-vaccinated children towards urban environments is envisaged [3].

The COVID-19 pandemic was declared a public health emergency of international concern in early 2020, and as of February 2023, over 755 million cases and 6.8 million deaths were reported [4]. Routine immunization faced backsliding of coverage due to the pandemic with more than 5 million additional zero-dose and under-vaccinated children added to the 2019 baseline globally. Disruptions to routine immunization occurred on a global scale, with low- and middle-income countries being the hardest hit, due to less resilient routine immunization systems. National lockdowns and restrictions of movements interrupted the provision of medical services and resulted in large swaths of the population either not having access to services or feeling nervous to access these services due to fear of COVID-19 transmission. Pakistan and India are said to have reported major drops in immunization coverage, with Pakistan reporting a substantial coverage decline in all childhood immunization services during the pandemic lockdown [5,6]. Due to data limitations, the extent of decrease in service coverage in some African countries has not been fully elucidated. However, the trend appears to indicate that countries with lower pre-pandemic immunization coverage trends saw more significant drops in performance than countries with higher immunization rates [5]. The routine immunization coverage trajectories as of the end of 2021 indicate some level of recovery but still show warning signs that without concerted efforts to strengthen immunization systems, gaps in coverage will persist [5,7]

A 2022 estimation of the number and distribution of zero-dose and under-immunized children within remote-rural, urban, and conflict-affected locations from 99 LMICs, showed approximately 30% of zero-dose children are in urban and peri-urban areas, compared with remote-rural areas which have about 11% [8]. A substantial proportion of these zerodose or under-vaccinated children in urban settings are in slums and informal settlements, and these numbers are projected to increase with the current trends of rapid urbanization. These urban settings have their own context-specific challenges needing distinct approaches, including a larger proportion of transient or migrant populations, unclear catchment areas for health facilities, lack of appropriately disaggregated data, disenfranchised communities, increase in informal settlements, insecurity, and satisfying multiple stakeholders including private providers [3].

A major indicator of the Immunization Agenda 2030 (IA2030) [9,10] is a reduction in the number of zero-dose children by 50% by 2030, but this indicator is off-track in large part because of routine immunization backsliding. A total of 20 high-burden countries (Appendix A.1) are home to over 75% of the world's zero-dose children as of 2021 [11]. These countries are largely urbanized, with a considerable proportion of their zero-dose children localized in urban settings, as exemplified by 4 of these 20 focus countries accounting for over 50% of the global population of zero-dose children. These countries include Brazil, Mexico, Indonesia, and Nigeria, with 87%, 81%, 57%, and 53% urbanization, respectively [12]. Many countries have developed urban-specific immunization strategies or highlighted urban approaches in their comprehensive multi-year plan for immunization (cMYP) or national immunization strategies (NIS). Some of these countries attribute

their quick recovery from the COVID-19 pandemic to an active urban approach being implemented in their countries.

To address issues of urban immunization, the Urban Immunization Working Group (UIWG) was established. The UIWG is an extra-organizational group comprising policy, program, and academic experts, representing their respective organizations, created to inform global, regional, and national/subnational discussions on immunization equity in urban areas [13]. The group meets virtually or in person 2–4 times every year, facilitated by UNICEF, and has broad membership across key immunization stakeholders. In addition to fostering collaboration and alignment among partners working to improve immunization coverage in urban settings, the urban immunization toolkit, which is now being used by many, is one of the group's products. The urban diagnostic research across several countries was also supported by the working group. The group continually discussed emerging issues and defined a trajectory for future engagement to strengthen the focus on immunization in urban settings.

To facilitate getting countries back on track toward achieving the IA2030 goals, this paper highlights the importance of a renewed focus on addressing the idiosyncrasies of immunization in urban settings through a review of existing data and information on (i) the estimated magnitude of coverage backsliding in urban and peri-urban settings in a select set of countries, (ii) key issues affecting routine immunization in urban and peri-urban settings, and (iii) effective pro-equity strategies for routine immunization recovery in urban settings. The outcome of this study will be shared with global and national immunization stakeholders to provide evidence on effective strategies to vaccinate children in urban-poor communities.
