In response to recent allegations relating to gain of function and directed evolution research, Pfizer denies conducting such research in its ongoing development of the Pfizer-BioNTech COVID-19 vaccine. Research has been conducted with collaborators where the original virus has been used to express the spike protein from new variants of concern that have been identified by public health authorities. From this research, an existing vaccine can be quickly assessed for its efficacy. When a full virus does not contain any known gain of function mutations, the virus may be engineered to enable assessment of antiviral activity in cells. All antiviral products are required to undergo studies under U.S. and global regulations.