In recent years, global health policymakers have intensified efforts to understand and improve childhood vaccination coverage, recognizing its pivotal role in preventing infectious diseases and ensuring equitable healthcare access. A groundbreaking study by Cai, Zhou, Du, and their colleagues, published in the International Journal for Equity in Health in 2025, offers unprecedented insight into how sex and birth order independently and interactively influence vaccination rates for vaccines outside China’s national immunization program. This large-scale cross-sectional analysis unravels complex sociocultural and demographic dynamics that shape immunization in one of the world’s most populous nations.
China’s immunization landscape is unique, encompassing a comprehensive National Immunization Program (NIP) that provides free vaccines against major childhood diseases, and supplementary non-NIP vaccines, which are often optional and self-paid. While broad NIP coverage approaches near-universal levels in many regions, non-NIP vaccine uptake is highly variable, influenced by social norms, parental decision-making, economic factors, and public health policies. The study specifically dissects these non-NIP vaccines, exploring how factors like the child’s sex and their ordinal position among siblings correlate with vaccination rates.
The researchers employed data from an extensive national survey capturing vaccination status for children across diverse urban and rural communities. Utilizing sophisticated statistical models, the study examined independent and joint associations of birth sex and birth order with the likelihood of receiving individual non-NIP vaccines. Importantly, this approach goes beyond isolated factors to analyze how intersectionality between these variables might compound or mitigate inequities.
Their findings are striking and carry profound implications. The study reveals a consistent gender disparity, with male children more likely than females to receive non-NIP vaccines. This pattern echoes broader societal preferences ingrained in certain cultural contexts, where sons often receive preferential healthcare investment. Such biases undermine gender equity efforts and signal the need for targeted interventions to ensure girls are not disadvantaged in preventive health measures.
Equally notable is the influence of birth order. Firstborn children were found disproportionately more likely to be vaccinated with non-NIP vaccines compared to their later-born siblings. This trend may be explained by resource dilution theory, wherein parental attention, time, and finances are concentrated more heavily on the eldest child, detracting from subsequent siblings’ healthcare access. The research quantifies this phenomenon within the contemporary Chinese setting, shedding light on how family composition subtly shapes immunization behaviors.
Crucially, the study pioneers in evaluating the interaction between sex and birth order, uncovering complex joint effects. For instance, the disadvantage experienced by female children is exacerbated further if they are later-born rather than firstborn, compounding vulnerability to under-vaccination. This multi-layered inequality underscores that simplistic one-dimensional analyses miss critical nuances, and policies must factor in overlapping social determinants to be effective.
From a public health perspective, these findings emphasize the urgency of multifaceted strategies to close coverage gaps. Interventions could include community education campaigns challenging gender norms, financial subsidies for vaccines targeted at vulnerable birth order groups, and strengthening primary healthcare outreach tailored to families with multiple children. Additionally, advocating for inclusion of key non-NIP vaccines in the national program might reduce financial barriers and normalize their uptake across all demographics.
The study’s methodology merits attention. By leveraging a robust nationally representative dataset combined with advanced multivariate analysis, the authors achieved precise estimation of effect sizes while controlling for potential confounders such as socioeconomic status, geographic variation, and parental education. This rigor enhances confidence in the validity and generalizability of the findings across China’s heterogeneous population.
Furthermore, the researchers discuss potential mechanisms underlying the observed disparities. Behavioral economic theories suggest parental risk perception varies by child sex and family dynamics, influencing proactive health decisions. Cultural anthropology perspectives underscore persistent son preference in some communities, linked to long-standing social structures and inheritance norms. Understanding these undercurrents is vital to designing culturally sensitive interventions that resonate deeply with affected families.
One of the study’s strengths is its focus on non-NIP vaccines, which have received comparatively limited attention in the literature, despite their growing importance. These vaccines, including those against pneumococcus, rotavirus, and human papillomavirus, can substantially reduce morbidity but require out-of-pocket payment, making their equitable distribution challenging. By illuminating differential uptake patterns for these vaccines, the study fills a critical knowledge gap.
The public health implications extend beyond China. Similar gender and birth order biases may exist in other middle-income countries with rapid healthcare transitions and unequal resource distribution. Thus, the study’s framework and conclusions can guide international efforts to improve pediatric vaccine coverage globally, contributing to the Sustainable Development Goals related to health equity.
Critically, the researchers caution that cross-sectional design limits causal inference but underscore consistency with previous qualitative and quantitative studies supporting gender and birth order impacts. Longitudinal research could further unravel causality and evaluate intervention effectiveness. Meanwhile, their findings offer a compelling evidence base for immediate policy attention.
In an era where vaccine hesitancy and health inequities threaten progress, nuanced understandings such as those provided by Cai et al. are invaluable. They remind us that raising vaccination coverage transcends medical technology – it demands social insight, cultural empathy, and intelligent policy frameworks attuned to diverse family and societal realities.
Moving forward, multi-disciplinary collaboration among epidemiologists, sociologists, health economists, and policymakers will be key to translating these insights into effective programs. Tailored messaging that acknowledges family preferences, behavioral drivers, and economic constraints can foster more inclusive immunization practices. Ultimately, achieving equitable vaccine coverage protects all children, strengthens pandemic preparedness, and promotes healthier societies.
This pioneering research thus opens new avenues for vaccine equity science, inspiring deeper inquiry into how fundamental aspects of child identity—sex and birth order—shape health outcomes. The findings prompt reevaluation of existing immunization policies and invigorate global discussions on optimizing childhood disease prevention in complex social landscapes. As vaccination remains a cornerstone of public health, ensuring every child’s equal access is both a moral imperative and pragmatic necessity.
Subject of Research: Associations of sex and birth order with coverage of non-national immunization program vaccines among Chinese children.
Article Title: Independent and joint associations of sex and birth order with non‑national immunization program vaccine coverage among Chinese children: a cross-sectional analysis.
Article References:
Cai, H., Zhou, Y., Du, A.H. et al. Independent and joint associations of sex and birth order with non‑national immunization program vaccine coverage among Chinese children: a cross-sectional analysis. Int J Equity Health 24, 131 (2025). https://doi.org/10.1186/s12939-025-02502-6
Image Credits: AI Generated
