The term "gain of function" is often taken to refer to research with viruses that puts society at risk of an infectious disease outbreak for questionable gain. Some research on emerging viruses can result in variants that gain the ability to infect people but this does not necessarily mean the research is dangerous or that it is not fruitful. Concerns have focused on lab research on the virus that causes bird flu in 2012 and on the virus that causes COVID-19 since 2020. The National Institutes of Health had previously implemented a three-year moratorium on gain-of-function research on certain viruses, and some U.S. legislatures have proposed bills prohibiting gain-of-function research on "potentially pandemic pathogens."