Sanofi (SNY 2.28%) may be late to the coronavirus vaccine game, but it has a good excuse for finally launching the first phase of its clinical trial program: The French drugmaker is using a traditional protein-based approach to develop its coronavirus vaccine.

Moderna (MRNA 0.69%) and BioNTech (BNTX 1.64%) -- both more than halfway through enrolling their respective phase 3 clinical trials -- were able to move more rapidly from concept to a vaccine candidate ready for clinical trials because they're using a new approach called messenger RNA (mRNA). The technology allows for easy manufacturing of an mRNA that codes for a protein for the coronavirus. Then the patient's cells do the hard work, using the mRNA to express the viral protein inside the patient.

The more traditional approach that Sanofi has taken required the company to figure out how to manufacture and purify the viral protein expressed in cells in a bioreactor. Proteins are a lot more variable than mRNA, making the manufacturing setup a time-consuming process.

Gloved hands giving an injection into a shoulder

Image source: Getty Images.

In April, Sanofi enlisted the help of GlaxoSmithKline (GSK -0.19%), which has an established pandemic adjuvant technology designed to boost the immune response to the vaccine. The companies expect to be able to manufacture enough of the vaccine and the adjuvant to create 1 billion doses in 2021.

Sanofi, which is leading the clinical development, plans to enroll 440 participants in the phase 1/2 study, with initial data expected in December 2020. At that point, Sanofi and GlaxoSmithKline hope to be able to start a phase 3 clinical trial, which would potentially allow the duo to apply for regulatory approval in the first half of 2021.

While taking longer in preclinical development, Sanofi's protein-based technique is a proven technology that is also used in its flu vaccine, which will hopefully increase the likelihood of success if Moderna's and BioNTech's newer technology stumbles.