In the case of the mRNA vaccines (e.g. Pfizer) it is the spike protein targeted, and that has a hard time effectively mutating because most changes to it make i

In the case of the mRNA vaccines (e.g. Pfizer) it is the spike protein targeted, and that has a hard time effectively mutating because most changes to it make it less infectious. Other aspects of the virus may change but the spike so far has been relatively stable.