A clinical-trial failure for Pfizer and BioNTech means Moderna is leading the race to develop a combo shot for the flu and COVID-19.Pfizer (PFE -1.43%) and BioNTech (BNTX -2.36%) recently fell behind in their race with Moderna (MRNA 0.25%) to develop new combination shots that could be worth billions in annual sales. Top-line results from an experimental vaccination to protect against influenza and COVID-19 weren't a complete disaster, but there isn't much room for error when it comes to vaccine development ...