On Friday, Sanofi announced a new effort to develop a vaccine to prevent the novel coronavirus, Covid-19. A collaboration with the biotech firm Translate Bio, the program will be at least the fourth known effort to build a Covid-19 vaccine using messenger RNA, a previously little-known vaccine development method.

The collaboration is Sanofi’s (ticker: SNY) second Covid-19 vaccine program. Translate (TBIO) is the last of the four biotech firms best known for working on mRNA-based therapies to announce it is working toward a...