The spike protein "springs" into an elongated configuration to help it latch onto a cell wall. Several of the vaccines have purposefully modified the protein us

The spike protein "springs" into an elongated configuration to help it latch onto a cell wall. Several of the vaccines have purposefully modified the protein used in the vaccine to keep it in it's unsprung form. The idea is that you want the antibody response to be focused on the unsprung protein so that you can prevent it from attaching and springing in the first place. From what I understand, the vaccine researchers have tested several variations of the spike protein in animal models to try to select one that will yield the best antibodies. The immune system is quite complex, but in theory it would be possible to design a protein that resulted in better antibodies than a wild infection. An analogy is it's like showing your immune system a lock and asking it to come up with a key that opens the lock. A different lock might produce a universal key that opens many locks.