Vaccine uptake has been declining in Brazil and South Africa over the last decade. This decline has reversed important gains in protecting children against vaccine-preventable diseases such as measles, polio, diphtheria and whooping cough.Both countries have well-established, universal and free childhood immunisation programmes. In Brazil, coverage has dropped 10-20 percentage points since 2016 and remains below the 95% target for several routine vaccines. In South Africa, vaccination coverage has steadily declined since 2015. For example, coverage for the first dose of measles-containing vaccine (MCV1), a key indicator of immunisation programme performance, decreased from 86% in 2015 to 76% in 2024. Reasons include social conditions, personal experiences, cultural beliefs, and access to health services. These vary across groups and contexts.As researchers in public health, we have studied how these different social contexts shape routine childhood immunisation in Brazil and South Africa.The study formed part of the PhD research of physician and lecturer Camila Matos, conducted under the supervision of professors Marcia Couto in Brazil and Charles Shey Wiysonge in South Africa.Participants were recruited from diverse racial, gender and socioeconomic backgrounds. The analysis considered how these social determinants influenced the decisions they made about health. It found that vaccine hesitancy in the two countries is not a single, uniform phenomenon.The research found that practical barriers to vaccination mattered most for lower-income families in both countries. Among the barriers were long waiting times, limited clinic hours, transport difficulties, and occasional vaccine shortages. In contrast, among some higher-income and more educated families in both countries, vaccination decisions were more likely to reflect values. Decisions were more about vaccine safety and side effects, distrust of pharmaceutical industries, and parental autonomy.Country-specific concerns also emerged, including fears about autism or personality changes in South Africa and concerns in Brazil about the large number of vaccines and doses in the childhood immunisation schedule.The findings show that decisions about vaccination are shaped by different social realities. These include inequality, access to health services, trust in institutions, and exposure to misinformation. Recognising differences is important for developing vaccination policies and communication strategies that respond to local contexts.Declining vaccine coverageBrazil and South Africa are upper middle-income countries, both with long histories of social inequality and segregation. Brazil has the National Immunisation Programme and South Africa has the Expanded Programme on Immunisation. Both have historically achieved high vaccination coverage. Brazil maintained coverage above 95% for several childhood vaccines during much of the 2000s and early 2010s. South Africa has frequently reported national coverage levels around or above 90% for key childhood vaccines before recent declines.But both countries are now facing sustained declines in vaccination coverage. Brazil’s decline is due to a combination of factors including social inequalities, disruptions caused by the COVID-19 pandemic, barriers in access to health services, and growing vaccine hesitancy. In South Africa, too, the decline is due to a combination of factors. Persistent inequalities in healthcare access and increasing vaccine hesitancy leave a substantial proportion of children not fully immunised. In 2016, an estimated 40.8% of children were not fully immunised for their age. The COVID-19 pandemic also disrupted routine vaccination services. Coverage of key vaccines remained below pre-pandemic levels.Beyond misinformation: social roots of vaccine hesitancyEvidence from both Brazil and South Africa points to vaccine hesitancy as an important reason for declining vaccination coverage. Vaccine hesitancy is defined as “a motivational state of being conflicted about, or opposed to, getting vaccinated”. It includes intentions and willingness to vaccinate, but it is context-specific. We conducted in-depth interviews to explore how caregivers of children up to six years old perceived, delayed, selectively accepted or refused vaccines. Participants were intentionally recruited from diverse racial, gender and socioeconomic backgrounds.The broader study included families with different vaccination statuses and practices. These included children fully vaccinated according to the national schedule, children vaccinated with delayed or alternative schedules, and children who had received few or no vaccines. This article focuses on narratives in which vaccine hesitancy emerged as a central theme.We found that childhood vaccine hesitancy was influenced by different, but often interconnected, social and everyday life factors. Among many medium-low and low-income non-white families in both countries, vaccination uptake was affected by hesitancy-related concerns and practical difficulties in accessing vaccination services. These included long waiting times, limited clinic hours and, in some cases, temporary shortages or unavailability of vaccines at health facilities.These challenges rarely reflected outright refusal but led to delays and incomplete vaccination. In contrast, deliberate decisions not to vaccinate were more common among medium-high and high-income white families. These families emphasised parental autonomy, individual choice and natural lifestyles. They often positioned themselves as critical of the medical or pharmaceutical systems rather than explicitly anti-vaccine.Why vaccine hesitancy cannot be addressed with a single strategyAcross groups, concerns about safety and side effects were central. Many caregivers reported “doing their own research” online. This exposed them to misinformation while reinforcing a sense of autonomy. Yet mistrust was not confined to privileged families. Among lower-income participants, it often stemmed from negative experiences with health services.The findings also reveal country-specific nuances. In South Africa, some linked vaccines to conditions such as autism or personality changes. In Brazil, concerns were more related to the extensive immunisation schedule, the high number of doses, and the administration of several vaccines at the same visit.Together, the results show that one-size-fits-all strategies are unlikely to succeed. Effective responses must address both structural barriers and the cultural perceptions and social beliefs surrounding vaccination.We argue that the next steps should place the social sciences at the centre of immunisation policy. Public health planning must take account of community perspectives and the social determinants of vaccine hesitancy. Communication must be culturally responsive. Reducing vaccine hesitancy to “lack of information” or parental negligence is too simple. People’s decisions are shaped instead by complex realities. The study shows that choices about whether or how to vaccinate children are deeply rooted in the social positions families occupy. They intersect with race, class, inequality, trust, and lived experiences with health systems. Rebuilding confidence will depend on better information and socially responsive, context-aware public health strategies.The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.