The evolving epidemiology of SARS-CoV-2

Pandemics usually start with a bang following the emergence of a new pathogen that is both sufficiently infectious and virulent to pose a substantial threat and warrant an emergency response. The very fact that a pandemic involves a new or substantially changed infectious agent means the initial response is hampered by limited epidemiological data and a large amount of uncertainty. It was in this context that COVID-19 infections spiralled in many countries in early 2020, overwhelming health systems and driving excess mortality. Without reliable data it was initially unclear who was most at risk of, and from, infection, or of transmitting the virus to others. Over the course of the pandemic global research efforts have gradually pieced together the complex epidemiology of SARS-CoV-2 infections and longer-term sequelae, but there is still much work to be done. The situation also continues to evolve as the virus mutates, public health responses change, effective treatments become available, and population level immunity is acquired and matures. Although the onset of a pandemic is usually explosive and undisputed, the end is rarely as dramatic or as certain. Tracking the changing epidemiology of SARS-CoV-2 in the transition from pandemic to endemic is essential and remains a significant task.