Vaccine specialists Sanofi SA and Glaxosmithkline plc have been behind the curve throughout the pandemic, with upstarts such as Moderna Inc. and Biontech SE stealing the show with their ground-breaking mRNA technology. While their rivals were beginning to launch the first wave of vaccines early last year, Sanofi and GSK had to reformulate theirs after it failed to produce a strong enough immune response in older people. New results show that the shot, SP-0253, could play a role as a booster but there will be another delay after the companies struggled to recruit enough participants in a crucial phase III trial.