Moderna's mRNA flu vaccine faces challenges in early success and revenue expectations.

Moderna's experimental flu vaccine did not meet the criteria for "early success" in a late-stage trial, and its shares fell 3%. The company expects to have six major vaccines on the market in the next few years, with its COVID-19 shot currently being the company's lone marketed product. Moderna is banking on its respiratory vaccine candidates to help offset the expected steep fall in revenue from its hugely successful COVID-19 vaccine. The company's decision to continue the trial comes months after data from an earlier trial showed the shot generated a strong immune response against influenza A strains, but failed to generate a similar response as the approved vaccine for less-prevalent influenza B.