It has gone through significant mutations, but there are a lot of places that it hasn't changed. When you respond, it's to all of the different pieces that are on the spike protein. That's why it still works against serious disease, against omicron, if you have been immunized. You're not going to die at the same rate, and you're not going to have hospitalization at the same rate.
On June 1st, 2022. See this statement in context.