Measles is a serious disease with life-altering and life-threatening consequences. During 2019, New Zealand experienced a measles epidemic with over 2000 confirmed cases. The epidemic was concentrated in the Auckland region where more than 80% of cases occurred and children aged less than 2 years comprised 25% of cases. The high rate of hospitalised children and reportedly severe disease in Auckland was unexpected. Emerging evidence demonstrates an immune-deficient state lasting for years following measles infection in children and leading to increased risk of other infectious diseases. Using health datasets along with specific immune testing among young children who have recovered from measles, we will explore why our measles was more severe and the risk of future illness left after measles recovery. Understanding the drivers of measles severity and longer-term sequelae will help to build health response and target prevention strategies, reducing the acute and long-term negative impacts from current and future epidemics.