Previously it wasn't deemed necessary (i.e. the original design was good and universal enough), for Omicron as far as I know tests are running, depending on how

Previously it wasn't deemed necessary (i.e. the original design was good and universal enough), for Omicron as far as I know tests are running, depending on how that goes and how countries decide to treat the regulatory part of updating it we might see an adjusted one now. (EDIT: "universal enough": we don't want a vaccine extremely optimized for a variant, but one that has a good chance to work well against other/new variants too, so there's a balance if a improvement against one variant makes it worse overall) EDIT 2: apparently some small trials for modified variants are also running for Delta, so I guess this statement needs to be modified and it wasn't considered justified to rush out a new anti-delta variant, but testing is done so the findings can be used for upgrades.