GSK SanofiSanofi (NYSE:SNY) and Glaxo Smith Kline (NYSE:GSK) are moving forward with their development plans of a COVID-19 vaccine.

In December, the two companies announced that their vaccine development efforts had been delayed after the product failed to mount a robust immune response in older adults.

The two companies believe the setback resulted from an insufficient amount of the antigen in the vaccine. They have since revised the formulation and have launched a Phase 2 study to test the adjuvanted recombinant protein-based COVID-19 vaccine candidate.

If the study meets its primary endpoints, the companies will launch a Phase 3 trial in the second quarter of the year with authorization potentially following in the fourth quarter of the year.

“We are confident that our vaccine candidate has strong potential and we are very encouraged by the latest preclinical data,’ said Thomas Triomphe, executive vice president and head of Sanofi Pasteur, in a statement.

GSK is also collaborating with the German CureVac (NSDQ:CVAC) to develop an mRNA vaccine for SARS-CoV-2 variants.