Why Reaching Zero-Dose Children Holds the Key to Achieving the Sustainable Development Goals

"There were 18.2 million zero-dose children in 2021, and as they accounted for over 70% of all underimmunized children, reaching zero-dose children will be essential to meeting ambitious immunization coverage targets by 2030."

While certain geographic locations, such as urban slum, remote rural, and conflict-affected settings, may place a child at higher risk of not receiving any routine immunisations, zero-dose children are found in many places, and understanding the social, political, and economic barriers they face will be key to designing sustainable programmes to reach them. This article explores these barriers and explains why reaching zero-dose children and missed communities is critical to achieving the Sustainable Development Goals (SDGs) commitment to "leave no one behind".

As detailed here, while many life-saving vaccines have been added to national immunisation schedules, some children continue to be deprived of the benefits of even the most basic vaccines in almost all countries. However, in 2021, 6 large-population countries - namely, India, Nigeria, Indonesia, Ethiopia, Philippines, and the Democratic Republic of the Congo (DRC) = accounted for half of all zero-dose children. Roughly 40% of zero-dose children live in settings highlighted by the Equity Reference Group on Immunization (ERG) - urban, remote rural, and conflict-affected settings - with the remaining living in non-urban rural settings.

The Immunization Agenda 2030 and the supporting Gavi 2021-2025 Strategy have ambitious targets to reduce the number of zero-dose children by 25% by 2025 and 50% by 2030 as compared to 2019 levels. However, empirical studies have confirmed that zero-dose children and their families face multiple barriers to obtaining immunisation, and their presence in a community is often an indicator of compounded inequities. For instance:

• Gender-related barriers: Theoretically, if barriers to immunisation related to women's empowerment could be overcome, there would be 4.7 million fewer zero-dose children globally.
• Poverty: Low-income countries have a 14 percentage point difference in median zero-dose prevalence when comparing the economically poorest to wealthiest household quintiles. Two-thirds of zero-dose children live below the poverty line of $US1.90 per day.
• Ethnicity and religion: For example, children from smaller ethnic groups in a country are more likely to be zero-dose than children in the dominant ethnic group. In 27 of 66 countries studied, children from the majority religion tended to be less likely to be zero-dose than children from minority religions, with the exception of countries where Muslims were the majority religion.
• Refugee, migrant, and nomadic populations: While some of these populations experience lower immunisation rates, it is context-specific with unclear patterns overall.
• Multiple deprivations: In an expanded analysis considering broader development indicators at the individual level, a lack of vaccination was strongly associated with lower access to improved water (prevalence ratio (PR) = 2.60) and sanitation (PR = 1.35), higher rates of childhood stunting (PR = 1.32), lower levels of maternal education (PR = 2.27), and lower levels of maternal demand for family planning satisfied with modern methods (PR = 1.42).
• Stigma and discrimination: These factors can determine whether a child benefits from vaccines.

The Identify-Reach-Monitor-Measure-Advocate (IRMMA) framework offers a way to develop strategies to reach zero-dose children and missed communities. This framework involves diving deeper into subnational- and community-level inequities and identifying where unvaccinated children live and what barriers to immunisation they face. Tailored strategies appropriate for the local context then need to be designed and operationalised. For example, strategies to sustainably reach zero-dose children with immunisation services in urban slums would be different from those for nomadic populations or for children in cross-border settings. This work will often require addressing gender barriers to immunisation, and opportunities for integrated service delivery should be sought out to increase efficiency and sustainability and to take advantage of opportunities opened by vaccination. Robust monitoring and measurement are critical for refining delivery approaches and advocating for pro-equity investments. Political will is necessary to initiate and sustain the programme and should be secured with a purposeful and inclusive advocacy approach.

A modeling study focused on 41 low- and middle-income countries (LMICs) from 2021 to 2030 estimated that vaccination among the two economically poorest wealth quintiles would avert 1.2 to 3.8 times as many future deaths per person vaccinated as compared to vaccination in the two wealthiest quintiles. The same study projected that vaccination would avert 24 million cases of medical impoverishment in 2021-2030, with more than 40% of the impact occurring within the economically poorest quintile for many vaccines. Sustainably reaching communities currently missed by immunisation would also help prevent future outbreaks, including the resurgence of measles and polio, and remove the need for repeated disease-specific supplemental immunisation activities.

In conclusion: "As zero-dose children and their families face multiple deprivations, with a high burden of morbidity and mortality, the potential for impact is great if they can be reached. By doing so, countries would be taking a key step toward ensuring no one is left behind in the Sustainable Development Goal era."