The mRNA vaccines have a turnaround of only a few weeks to produce a variant booster, so this is less of a concern than with older vaccine technologies. Moderna and Pfizer are currently trialing their SA strain booster that was formulated and produced in under a month [1][2].
[1] https://www.cnbc.com/2021/02/24/moderna-covid-vaccine-booste... [2] https://www.statnews.com/2021/02/25/is-more-simply-better-wh...