The term refers to laboratory techniques used to enhance aspects of a pathogen to make it more deadly and transmissible. This is usually done via a combination of gene editing and infecting several animal hosts. The aim is to learn how a pathogen may mutate and develop vaccines and therapeutics to stop its spread.
Deeper dive
In 2017, the National Institutes of Health announced that it would renew funding for gain-of-function projects after a three-year ban to give the federal government time to develop a framework for safely permitting gain-of-function research. The decision was controversial as some in the research community feared that there was no way to guarantee the safety of such research.
Gain-of-function research was occurring at a research facility in Wuhan, China where the SARS-CoV-2 emerged at the end of 2019, spawning ongoing questions about whether the virus originated from a research project gone wrong, or from an animal that spread it to people. (The majority of new diseases are caused by a jump from animals to people, a term called zoonotic disease.) The latest research published in summer 2022 suggests that SARS-CoV-2 emerged from an animal and not from a lab.