The Texas scientists, clad head-to-toe in protective gear, work in secure biosafety laboratories. They start with the original strain of coronavirus, the virus isolated in Snohomish County, Wash., nearly two years ago. They synthesize the omicron spike gene, with its dozens of mutations. Using the original virus as a scaffold, they swap in the new spike — steps they’ve done for alpha, beta, gamma, delta — and now omicron.