Sanofi and GSK said in a statement that the vaccine would be ready to begin testing in humans in the second half of 2020 and that they aim to complete all of the work required to file for regulatory approval by the second half of 2021.

The new vaccine will combine a vaccine technology that Sanofi currently uses to make a flu vaccine, FluBlok, with GlaxoSmithKline’s adjuvant, an additive that increases the potency of vaccines, making them more likely to be effective and easier to manufacture in large quantities.

Unlike most flu vaccines, which are manufactured in chicken eggs, the FluBlok vaccine is made using a genetically modified virus in cultures of cells from the fall armyworm, a type of moth. The cells are used to produce a protein identical to one on the surface of the virus, which the immune system learns to recognize and attack. The Food and Drug Administration approved the FluBlok vaccine in 2013. Sanofi bought Protein Sciences, which developed the vaccine, for $750 million in 2017.