Sanofi (NASDAQ:SNY) and Translate Bio (NASDAQ:TBIO) are joining the crowd of companies searching for a vaccine for SARS-CoV-2, the coronavirus that causes COVID-19. That's a crowd that certainly can't have too many participants at this point in the pandemic.

The two companies have been working together since 2018, when Sanofi paid Translate Bio $45 million upfront to develop messenger RNA (mRNA) vaccines for up to five undisclosed infectious disease pathogens. The deal also included the potential for an additional $760 million in milestone and option exercise fees for Translate Bio, as well as tiered royalty payments.

The coronavirus vaccine partnership is a separate arrangement for which financial terms weren't disclosed.

Gloved hands about to inject someones shoulder

Image source: Getty Images.

As you may remember from your high school biology class, messenger RNA strands are the intermediaries between DNA and the proteins they encode for. An mRNA vaccine codes for a protein found on the surface of a specific pathogen. The vaccine causes the patient's cells to produce the protein, which (hopefully) their immune system then recognizes as foreign. If it does, it will develop antibodies against that protein which should also protect the patient against the real pathogen.

This is the same technology that allowed Moderna Therapeutics (NASDAQ:MRNA) to move its SARS-CoV-2 vaccine candidate, mRNA-1273, so quickly into a clinical trial. BioNTech (NASDAQ:BNTX) and Pfizer (NYSE:PFE) are also developing an mRNA-based SARS-CoV-2 vaccine candidate, BNT162.

Translate Bio has already started production of multiple mRNA vaccine candidates, and is working with a contract manufacturer to scale up production once the lead candidate is established. Sanofi and Translate are hoping to have a clinic-ready candidate by the end of 2020 or in early 2021,  Maura Gavaghan, Translate Bio's associate director of corporate communications, told The Motley Fool.

Sanofi is also attempting to develop a more traditional, protein-based vaccine against SARS-CoV-2 -- that effort is being supported by the federal government's Biomedical Advanced Research and Development Authority. Protein-based vaccines are a more proven approach, but it takes more time to develop them.