**3. Discussions**

### *3.1. The Challenge: Historic Backsliding in Routine Immunization Coverage*

Across the world, the COVID-19 pandemic has disrupted essential health services, adversely impacting significant gains in health outcomes achieved in recent decades. This is particularly so for routine immunizations, with recently published WHO-UNICEF estimates showing historic reductions in immunization coverage in 2021, with 25 million children missing out on life-saving vaccines, the highest number since 2006 [1]. The number of 'zero dose children' (those who did not receive any dose of Diphtheria, Tetanus and Pertussis (DTP) containing vaccines) [2] increased sharply from 13 to 18 million during the pandemic period, a shocking 37% increase since 2019. While immunization coverage dropped in all WHO regions, some regions were more affected than others, with coverage dips ranging between 1% in Europe to as high as 9% in South-East Asia.

As a result of this monumental drop in coverage, a disproportionate number of children in low- and middle-income countries are left most vulnerable to vaccine-preventable diseases. With rising immunity gaps, the risk of large outbreaks is imminent, with cases of measles already reported in Africa and Eastern Mediterranean, and wild polio virus 1 (WPV1) detected outside the endemic countries in Asia [3]. This threatens the lives of unprotected children and could be severely disruptive to already over-stretched health services. Furthermore, some specific newly introduced antigens like Human Papillomavirus (HPV) vaccines are also seen to be more adversely impacted and less resilient to these shocks. Over the last two years, HPV vaccine coverage dropped by 15% [1]. Since 2019, 3.5 million eligible girls have not yet received their first dose of HPV vaccine, the highest decline since 2010. The trend is compounded by the fact that 59% of cervical cancer cases occur in countries that have not yet introduced HPV vaccination into their national programs, leaving millions of adolescent girls unprotected against cervical cancer.

Routine immunization programs were impacted by a 'double burden' of managing the disruptive effect of the COVID-19 pandemic as well as the subsequent historic COVID-19 vaccination efforts to improve population immunity against the virus. Nearly all countries reported some form of disruption to routine immunization (RI) services in 2020 and early 2021, with primary and community care among the most affected service delivery settings [4]. In many countries, several planned outreaches and even Supplementary Immunization Activity (SIA) were either suspended or postponed. In early 2021, more than one third of countries (37%) participating in surveys monitoring pandemic impact on health systems still reported disruptions to their routine immunization services in comparison to early 2020 [4].

Despite these sobering trends, some countries improved vaccination coverage during the pandemic—39 countries recovered or almost recovered to pre-pandemic levels in 2021. But over two years, only 24 countries achieved higher coverage in 2021 than in 2019 [5]. This notable progress is attributable to the intensification and mitigation efforts of country programs to maintain and/or resume vaccine delivery to catch up on missed populations. In some cases, these countries have managed to also attain high COVID-19 vaccination coverage—the fastest and one of the most complex global vaccine campaigns in history.

#### *3.2. The Opportunity: Restoring Coverage and Strengthening Program Resilience*

The vulnerability of global immunization systems demonstrates the urgent need to maintain, restore, and strengthen routine immunization systems in order to address the widening immunity gap in the context of the pandemic and build resilience for future shocks. Despite the complexities of managing immunization programs during a continually evolving pandemic, several countries have shown that improving immunization coverage is possible. Documenting and spotlighting learnings from these countries will help other countries to adopt similar practices to increase vaccination equity.

This article presents examples from five selected countries—Cambodia, Cameroon, Kenya, Nigeria, and Uganda—that have either maintained or increased their Diphtheria, Tetanus, and Pertussis–containing vaccine (DTP3) coverage rates in 2021 compared to 2019/20 (see Figure 1). Through strong partnership with the Ministries of Health in these countries, CHAI and immunization partners have witnessed and supported their journey to recovery. Using the key actions for sustaining global immunization progress [6], which highlight the urgent steps necessary for sustaining immunization activities globally as a conceptual framework, we outline several exemplary strategies adopted by these countries over the past two years that contributed to favorable immunization outcomes—also see [File S1].

**Figure 1.** Graph representing DTP1/3 coverage levels in selected program countries—Cambodia, Cameroon, Kenya, Nigeria, and Uganda—between 2019 and 2021. It highlights that across these five countries, national coverage of DTP3 remained the same or increased between 2019 and 2021, showcasing the immunization systems' resilience to withstand shocks due to the COVID-19 pandemic. Source: 2021 WHO-UNICEF Estimates.
