Lay summary
Routine childhood immunisation rates have been suboptimal and have further decreased since the onset of the Covid-19 pandemic, thereby exacerbating pre-existing immunisation inequities by ethnicity and region. It is imperative to improve coverage, particularly for children of Māori and Pacific ethnicities and those with migrant and refugee backgrounds. Mātauranga Māori and complexity-informed designs offer a promising framework to explore dynamic relationships, unpredictability, and uncertainty within a health system. This multi-method research, underpinned by complexity science and informed by kaupapa Māori and Talanoa principles, will quantitatively and qualitatively analyse the interconnected factors influencing childhood immunisation uptake. By understanding which children are missing out and why from multiple perspectives, we can inform ways forward for equitable immunisation services that are also resilient to future health shocks.