mRNA Vaccines Are Taking on the Flu Now Several companies, including Moderna, have recently announced the start of clinical trials for the seasonal flu using mRNA vaccines. Alerts Moderna vaccines are prepared for application at a United States military vaccination center at Camp Foster on April 28, 2021 in Ginowan, Japan Photo: Carl Court (Getty Images) Vaccines based on mRNA, first used for covid-19, may soon protect people from the influenza virus as well. This week, Moderna announced the start of a phase I/II trial testing out its vaccine candidate for the seasonal flu. Ultimately, the company hopes to develop a combination vaccine that can offer protection against the flu, covid-19, and other common respiratory viruses at the same time.