Five years after COVID-19 changed daily life around the world, scientists and health authorities have learned a great deal about the virus, its symptoms, prevention, treatment, and long-term effects. Although the emergency phase of the pandemic has passed, COVID-19 continues to circulate and remains an important public-health issue. The experience of the past several years has also changed the way researchers respond to emerging infectious diseases. Vaccines, antiviral treatments, improved testing, and better understanding of long-term symptoms have all contributed to a stronger response. How COVID-19 Has Changed Since 2020 SARS-CoV-2, the virus that causes COVID-19, has continued to evolve. New variants have appeared over time, with some spreading more easily than earlier versions of the virus. At the same time, population immunity has increased through vaccination, previous infection,
