Our vet's issue the past year or so is getting the pet vaccines he prefers. Supply is limited, particularly for the 3-year rabies vaccine he prefers for cats. Has had no reaction issues with it, but it's hard to find. When push comes to shove and the 3-year timeline is up, he's been stuck using the 1-year vaccine, which he has seen cause various reactions in some cats. Our cats are due next month. Sigh.
Do your cats go outside? Ours are indoor, and getting old, so we are ignoring vaccines.