Adverse consequences of Vaccination (Part II)

Good day colleagues and friends, so today we are going to continue talking about the several consequences or reactions a vaccine (or several) may cause.

Injection Site-Associaed Sarcomas

Remember when I mentioned that I never give more than 2 vaccines in one visit, nor in the same site,  especially in cats?

Well I will explain to you the reason why. 

Most vaccine site reactions in cats resolve rapidly. In some cats, however, tumors have developed at these injection sites many months after injection. They have typically been found in the cervical/interscapular and femoral regions. The appearance of these tumors has coincided with the introduction of new potent, inactivated, adjuvanted vaccines such as those directed against rabies and feline leukemia. Most of these tumors are fibro sarcomas, but other types of malignant sarcomas have been observed. Epidemiological studies have linked the development of these tumors to vaccination.

Cats with fibro sarcomas occurring at sites where vaccines are currently administered were compared with cats that developed fibro sarcomas at non-vaccine injection sites.

Cats receiving FeLV vaccine were 5.5 times more likely to develop a sarcoma at the injection site than cats that had not received a vaccine. There was a lesser association with rabies vaccination.

Actually in Early studies it was calculated that 1 to 3.6 sarcomas developed per 10,000 FeLV and rabies vaccines administered. This means that the risk did increase with the number of doses of vaccine administered: 50% increase following 1 dose, 127% increase following 2 doses, and 175% increase following 3 or 4 vaccines given simultaneously.

Vaccine-associated sarcomas tend to occur in younger animals and tend to be larger and more aggressive than sarcomas arising at other sites.

In some studies injection site sarcomas developed on average 26 months after the last rabies vaccination given and 11 months after FeLV vaccination.

It must be pointed out, that the risks for developing  sarcoma are considerably smaller than the disease risk incurred by unvaccinated cats. Similar vaccination related injection site sarcomas have been reported in ferrets.

Most of these products are administered by the convenient subcutaneous route, as a result, an irritating adjuvant may persist at the injection site for a long time. However, tumor development has also been associated with the use of non-adjuvanted vaccines, as well as the presence of persistent sutures.

Fibroblasts are stimulated to proliferate at sites of chronic inflammation and wound healing. In some of these fibroblasts the sis oncongene is activated, the Sis oncongen codes for Platelet Derived Growth Factor (PDGF) receptor, and vaccine associated sarcomas have been found to express both PDGF and its receptor.

Lymphocytes within these tumors are also PDGF-positive. Lymphocytes within the vaccine associated sarcomas secret PDGF, which then serves as a growth factor for the fibroblasts.

This combination of abnormalities could result in the loss of growth control in the fibroblasts engaged in the chronic inflammatory process.

To reduce the possibility of tumors developing at vaccination sites, it is highly recommended that the vaccines given be administered at standardized sites on the animal (especially cats), and away from sites where tumor management is difficult.

For example on the caudal half on the right side for rabies vaccine, and for the FeLV vaccine on the caudal left side of the cat's body.

This is not necessary but it is a recommendation, and if it's possible, the site of the vaccine and the name of the vaccine should be recorded for each vaccine to help in assessing risk factors.

Let's remember that non-adjuvanted vaccines appear to induce much less severe irritation and present a correspondingly lower risk for tumor formation.

How do you manage to administer vaccines to your feline patients?

Have you had cases of cats developing a sarcoma due to vaccines?

Hopefully this post can be useful for you in the daily practice.

MVZ Carolina Pruneda