Researchers from Johns Hopkins have been studying the use of mRNA vaccines, which use synthetic molecules to teach the body's immune cells how to make antigens to fight diseases. The vaccines are replicating vaccines, using synthetic molecules rather than a live virus, and can be made in a matter of months. Unlike other vaccines, these vaccines can be created in just a few months. Researchers are also targeting mRNA technology for cancer vaccines as a potential source of personalized medicine. The technology could improve the effectiveness of flu vaccines and potentially make them more effective and better matched against other flu viruses during flu season. However, there is a growing debate about the future of these vaccines, with recent studies showing they do not cause fertility problems in women.