Monthly Archives: August 2015

Surprizing Answers to 2 Important Vaccine Questions


  1. Isn’t there a special rabies vaccine for cats that does not cause vaccine sarcoma cancer?

Yes, and no.

There is a line of vaccines (Purevax from Merial) that was developed with vaccine sarcoma cancer in mind. When vaccine sarcoma cancer was first recognized in the 1980s, it was thought that the adjuvants in the vaccine were responsible for inciting the cancer. (Adjuvants are chemicals that increase the immune response to the antigens in the vaccines) Purevax vaccines are made without adjuvants.

Unfortunately, two more recent studies (here and here) show that the non-adjuvanted vaccines are just as likely to cause cancer as other vaccines. In fact, it is now clear that it is not just vaccines that can cause these cancers. ANY INJECTION can cause a tumor if given to a cat that is genetically predisposed. Now, the term “vaccine sarcoma” has been replaced by “injection site sarcoma.”

  1. Is there a difference between the 1-year and 3-year Rabies vaccines?

Maybe, maybe not.

There are some rabies vaccines that are labeled to give 1 year of protection and others that are labeled to give 3 years of protection. However, the first time a rabies vaccine is given to a pet, by law, it is only good for 1 year even if a 3-year rabies vaccine is used.

Here’s an interesting case in point. The Purevax rabies vaccine was tested at one year after vaccination. (Testing involves exposing vaccinated cats and an unvaccinated control group to the rabies virus) It passed the test so was issued the 1-year label. This is why many veterinarians are vaccinating cats yearly for rabies.

Now, the vaccine was also tested at 3 years post-vaccination. Although the vaccinated cats did not die when exposed to rabies, the 3-year vaccine FAILED the test. The problem was that the unvaccinated cats did not get ill either. It turns out that the challenge was not effective and Merial had to start over.

So, Merial threw in some extra antigen (nobody knows how much more) and started the process again. Three years later the challenge study was a success and Merial recently came out with a Purevax 3-year rabies vaccine. Unfortunately, they charge 3 times more for it, making the vaccine prohibitively expensive.

Besides, as the studies mentioned above prove, the Purevax vaccines are no more effective at preventing injection site sarcomas than any other vaccine. The bottom line is that you should get your cat the 3-year rabies vaccine to cut the number of vaccines he gets.