I remember reading earlier this year that Pfizer and Moderna did, in fact, create vaccines for both the alpha and delta strains of the virus. They did this within a matter of weeks after those strains had been sequenced. But, AFAIK, this is where the process stopped. I think if the current vaccines had not proven effective against alpha and delta, then they would have proceeded to Stage 1 trials, just as they'll do (quite rapidly, one would hope) if omicron turns out to be substantially vaccine-resistant.