An adjuvant is a fancy word for something that assists. In my military career, the adjuvant helped the wing commander out. In my veterinary career, the adjuvant helps the body’s immune system respond to a vaccine. Adjuvants are used with killed vaccine. (Hmm, another blog question…) Rabies vaccines are most commonly given as killed – who wants the live rabies virus injected into their cat? However, in the last 10-15 years, cats have had increasing numbers of horrible tumors (sarcomas) at the location where the rabies vaccine was given for years. So, now some vaccine manufacturers are making rabies vaccine without adjuvant. These vaccines are modified live vaccines (yup, that blog is next). And, then there is the issue of Thimerosol. Thimerosol is a preservative in many killed vaccines that contains mercury. Mercury is linked to brain damage and autism in humans. Bottomline: there’s more than one type of vaccine, it matters a lot in cats what is in the rabies vaccine, and this is a great topic of discussion for you and your veterinarian.