Rather than getting all these vaccines repeatedly for bacterial or viral respiratory illnesses, perhaps a course of oral doses of ivermectin could be used.
Was the coronvirus/adenovirus treatment oral ivermectin for 5 days? That would probably work for all animals. Just need to figure out the dosage.
Subcutaneous if really necessary. But oral is obviously safer and easier.
I would use metronidazole and ivermectin for respiratory or digestive problems. Metronidazole or brand name Flagyl is used as a experimental treatment for chronnes disease.