Moderna Falls as Flu Shot Final-Stage Trial Gives Mixed Results

Moderna Inc. shares lost the most since December after its influenza vaccine yielded mixed results in a final-stage trial, raising questions about the drugmaker’s plan to seek US approval for the messenger RNA-based shot as soon as this year.

In a trial of over 6,000 adults 18 and older, Moderna’s experimental mRNA-1010 shot produced an immune response against influenza A, the most common type of the virus, that was at least as good as an existing vaccine, according to a statement Thursday after US markets closed. Against influenza B, Moderna’s shot failed to prove it was equivalent to the available ...