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Posted on 04-30-2014

Merial Purevax Rabies Vaccine is Temporarily Off the Market!

The rabies vaccine that we prefer for cats has gone off the market due to a production problem. It is unknown when  it will be available again, but Merial (the manufacturer) suggests that it will be unavailable until October. We prefer this particular vaccine because it is the only non-adjuvenated rabies vaccine on the market. 

Rabies is the most important zoonotic disease. Zoonotic diseases are the ones that can be transmitted from animals to humans. Vaccinating pets protects them from this fatal disease but also protects their humans. The most important function of veterinarians within the professional public health community is to protect our clients from this disease by ensuring that pets are vaccinated. 

Rabies vaccinations are killed vaccines. There are no live virus particles within the vaccine. The immune system is not strongly stimulated by most killed vaccines. To make them work better an "adjuvant" is added. The adjuvant is often an aluminum salt. This addition stimulates inflammation the site of the vaccination and results in a stronger immune response to the vaccine. Most pets develop a bump at the site of traditional rabies vaccinations. The owners notice this about 14 days after the injection. Typically the bump is soft, movable with the skin and does not appear to cause pain to the patient. In dogs and in the vast majority of cats, this bump goes away spontaneously within a month or so. In rare cats (far less than a fraction of 1% but the exact frequency is subject to debate)  a malignant transformation can occur at the vaccine site. This results in the formation of an aggressive fibrosarcoma that can ultimately be fatal to the cat. This was noted in the early 1990's when the use of adjuvanated rabies and leukemia vaccines in cats became common. This problem has not been documented in dogs. Extensive research has demonstrated that the adjuvant is the likely cause of this tumor. Merial Purevax is a non adjuvantated vaccine. In this case a canarypox virus has been modified, using recombinant technology, to produce expression of desired antigens capable of stimulating a protective immune response to rabies. Safety and immunogenicity of this product have been demonstrated by vaccination and challenge tests in susceptible cats. In the past 10 years veterinarians who use this vaccine in place of traditional adjuvanated rabies vaccines have seen a dramatic decrease in feline fibrosarcomas. This has been our experience at County Animal Hospital. 

The lack of availability of Purevax creates a dilemma. Do we withhold rabies vaccine and allow pets to become potentially susceptible to rabies, placing them and their human families at risk, or do we administer the traditional adjuvanated vaccine and risk inducing fibrosarcoma in our feline patients?

Our recommendation depends on your cat's lifestyle. For those cats that are strictly 100% indoors we recommend wait and see if Purevax becomes available soon. When you get a reminder card come in for your cat's annual examination  (that's important). When the vaccine becomes available we will notify you and you can come in for the vaccine and not have to pay for another office visit (unless  your cat has developed some medical issue that requires a veterinarian's examination). There is still risk that wild animals (especially bats) can enter your home so this is not ideal. If that risk seems unacceptable to you then we should vaccinate with the adjuvanated vaccine. Cats who go out (even infrequently or briefly) should absolutely receive the available adjuvanated (traditional) rabies vaccine when it is due. 

If you have any question about this call the office 845-634-4607. 

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