$Moderna (MRNA.US)$ stock gained 7.8% Thursday, its virtual R&D day, which began at 8 a.m. Eastern. It plans to announce the development of a vaccine candidate that will protect against Covid-19 and the flu, to be known as mRNA-1073. 
Moderna was a very different company at the time of its last virtual R&D day in September of 2020. Still a clinical-stage company at the time, Moderna had no authorized or approved products. That changed months later, when the U.S. Food and Drug Administration authorized Moderna’s Covid-19 vaccine, which is expected to bring in $20.1 billion in revenues this year alone.
Its stock price has been up more than 300% this year. 
Just to mention, another vaccine maker $Novavax (NVAX.US)$ had also initiated an early-stage study to test its combined flu and COVID-19 vaccine. However, the same scenario didn't show on its stock price. Kinda tricky.
Source: Moderna Stock Jumped Because It Just Unveiled a Two-in-One Vaccine for Covid and the Flu