The rapid production of safe, effective and consistent vaccines is essential for supporting COVID-19 immunisation programmes in the UK and globally. However, manufacturing vaccines is challenging for various reasons that include the complex processes involved, the specialist knowledge and experience required, and the natural variability of the biological materials and systems used. Urgent demand is leading to manufacturers and governments taking on significant financial risks in order to speed up production. What is the UK Government doing to accelerate vaccine manufacture? How are vaccines made? Why is manufacturing vaccines at large scales so challenging?