Sanofi and GSK will also study their vaccine's ability to work as a booster shot in people who had previously received another vaccine against coronavirus.The Phase 2 trials already showed a strong immune response after a single shot in participants who had previously contracted the coronavirus.Like most of the other jabs in circulation, the Sanofi-GSK vaccine would require two doses.The firms are combining a Sanofi-developed antigen, which stimulates the production of germ-killing antibodies, with GSK's adjuvant technology, a substance that bolsters the immune response triggered by a vaccine.If the trial becomes successful, the companies hope to launch their vaccine by the end of 2021 -- one year after Pfizer and Moderna jabs were approved.