The COVID-19 pandemic has brought advances in population health measurement at an unprecedented scale and speed. A study of time trends for long-term conditions, published in The BMJ (doi:10.1136/bmj-2025-086393), uses data from electronic health records from primary and secondary care. These data reveal dynamic changes in disease patterns as they occur. Traditionally, health care systems have relied on static estimates of the burden of disease that are published years after data collection. Rates of disease incidence and prevalence are held to be immutable truths, although they vary over time, demographics, and geography. Data from the study show how rapidly diagnostic activity changes and how variable responses to external pressures are. These data have implications for public health surveillance, research, and health care delivery.