Can't believe I had to scroll down this far to find this - but this is exactly true. Since the virus has a non-human animal reservoir that means that even if every human receives the vaccine, all it takes is re-transmission from the animal reservoir back into the human population after the immunity period expires.

This means we'll probably have to receive Covid vaccination on a regular basis along with the flu vaccine in order to maintain a permanent broad-scale immunity. At least until we have a radical new treatment for this family of viruses that can confer a "permanent" immunity - something that for now is in the realm of science fiction.