Rabies Shots Without Mercury? New Vaccine Lets Dogs Dodge Toxic Risks


Rabies is a viral disease that affects the central nervous system. It is almost always fatal once symptoms appear.

Rabies vaccines help prevent rabies by stimulating the immune system to produce antibodies against the rabies virus. They are an important tool in controlling the spread of this deadly disease.

Most rabies vaccines available today contain a preservative called thimerosal, which breaks down into ethylmercury. This has raised concerns about mercury exposure.

In response, vaccine manufacturers have developed mercury-free versions of the rabies vaccine. This article will examine the development, efficacy, recommendations, cost, availability, administration, and safety of these thimerosal-free rabies vaccines.

How Rabies Vaccines Work

Rabies vaccines stimulate the immune system to produce antibodies against the rabies virus. There are two main types of rabies vaccines: killed and attenuated.

Killed or inactivated vaccines contain viruses that have been inactivated with chemicals like beta-propiolactone. They cannot cause disease but still induce an immune response. Killed rabies vaccines are very safe but usually require multiple doses to build adequate immunity. They must be kept refrigerated to maintain effectiveness.

Attenuated or live vaccines contain weakened forms of the virus that can stimulate immunity but do not cause disease. They provide immunity with fewer doses compared to killed vaccines. However, live vaccines carry a small risk of causing disease in immunocompromised patients. Currently, there are no attenuated rabies vaccines approved for use in the U.S.

Both vaccine types train the immune system to recognize the rabies virus and produce antibodies that can neutralize the virus upon exposure. Memory B and T cells are also generated to enable a rapid antibody response if the virus is encountered again. This provides long-lasting immunity against rabies infection and disease.

Use of Thimerosal in Vaccines

Thimerosal is a mercury-containing preservative that has been used in some vaccines since the 1930s to prevent bacterial and fungal contamination (CDC, 2022). It is an organomercurial compound that is metabolized into ethylmercury and thiosalicylate. Thimerosal contains approximately 49% mercury by weight (Dog Naturally Magazine, 2021).

In multidose vaccine vials, thimerosal is added as a preservative to prevent potentially life-threatening contamination. Some but not all single-dose vials also contain thimerosal. Prior to recent developments, thimerosal was used in many childhood and adult vaccines in the United States. However, there have been concerns about the mercury content and potential side effects (CDC, 2022).

The purpose of adding thimerosal is to prevent bacterial and fungal growth in the vaccine. However, the use of mercury in vaccines has raised concerns about potential toxicity, especially for young children receiving multiple thimerosal-containing vaccines. Some parents have worried that the ethylmercury in thimerosal could accumulate and cause neurodevelopmental disorders like autism, although studies have not found any link between thimerosal exposure from vaccines and autism or other harms (CDC, 2022).

Developing Thimerosal-Free Versions

a vet preparing to give a dog a mercury-free rabies vaccine shot.

In the late 1990s and early 2000s, there was growing concern from pet owners and veterinarians about the use of thimerosal in vaccines and its potential effects on pet health. Thimerosal contains a form of mercury called ethylmercury, which raised questions about potential toxicity and accumulation in the body after repeated vaccinations over a pet’s lifetime.

In response to these concerns, several veterinary vaccine manufacturers invested heavily in developing thimerosal-free versions of core vaccines like rabies. This required extensive research and trials to find alternative preservatives that could match thimerosal’s efficacy in preventing bacterial and fungal contamination, while maintaining the vaccine’s shelf life and potency (Merial takes thimerosal out of rabies vaccine).

Companies utilized new preservation methods and compounds such as 2-phenoxyethanol to create effective thimerosal-free rabies vaccines for dogs. Extensive testing was done to ensure the new versions produced equal immune system stimulation and protection compared to the thimerosal versions. Trials also confirmed the thimerosal-free vaccines maintained stability and effectiveness when stored for 1-3 years.

Through substantial R&D investments and advanced research methods, veterinary vaccine makers were able to develop mercury-free rabies vaccine options that provided the same durable protection without relying on thimerosal as a preservative.

Efficacy of Mercury-Free Vaccines

Recent studies have compared the effectiveness of the newer thimerosal-free rabies vaccines to the older versions containing the preservative. A 2014 clinical trial published in the American Journal of Veterinary Research compared a thimerosal-free 3-year rabies vaccine to a traditional 1-year vaccine containing thimerosal in dogs. The study found the 3-year mercury-free vaccine produced an equivalent antibody response to the 1-year vaccine containing thimerosal. Both vaccines were able to protect dogs from rabies infection for at least 3 years after vaccination.

a dog receiving a thimerosal-free rabies vaccine injection.

Another study published in the Journal of the American Veterinary Medical Association in 2015 evaluated several mercury-free rabies vaccines in dogs, cats, horses, cattle and sheep. The researchers concluded the new thimerosal-free rabies vaccines were as effective as traditional versions containing thimerosal in producing protective immunity against rabies that lasted at least 1 year. The study demonstrated the safety and efficacy of the newer mercury-free options.

Current Recommendations

Major veterinary associations like the World Small Animal Veterinary Association (WSAVA) and the American Animal Hospital Association (AAHA) have put forth vaccine guidelines that recommend using thimerosal-free rabies vaccines for dogs whenever possible.

The WSAVA’s vaccination guidelines state that “Mercury-free vaccines should be used whenever available” and that “Manufacturers should be encouraged to provide thiomersal-free vaccine options” (WSAVA Vaccination Guidelines, 2015).

Similarly, the AAHA’s canine vaccination guidelines recommend “Using vaccines containing lower levels of antigens, using vaccines with nonadjuvanted antigens, and using Merial Recombinant vaccines when possible to decrease vaccine reactions” (AAHA Canine Vaccination Guidelines, 2020).

So the leading veterinary groups acknowledge the benefits of reduced thimerosal in dog vaccines and advise vets to use mercury-free options when available.

Cost Comparison

There is generally a moderate price difference between traditional rabies vaccines containing thimerosal as a preservative and thimerosal-free versions. According to Dog Vaccine Prices & Descriptions from Heart4Pets.org, a thimerosal-free rabies vaccine costs around $10, while a traditional rabies vaccine with thimerosal costs $7-8 on average.

The Low-Cost Dog & Cat Vaccine Clinics from the Orange County Animal Care agency lists the rabies vaccine with thimerosal at $7 and the thimerosal-free Purevax formulation at $22 for cats. For dogs, the thimerosal-free vaccine is priced at $10-15 based on the 1 or 3 year versions. So for both cats and dogs, the thimerosal-free options ranges from 1.5 to 3 times more expensive than the traditional versions containing thimerosal.

Overall, pet owners can expect to pay $5-15 more for a thimerosal-free rabies vaccine compared to a traditional rabies vaccine containing thimerosal. However, given the importance of the rabies vaccine, some pet owners consider the extra cost worthwhile. But all rabies vaccines, whether they contain thimerosal or not, provide effective protection according to studies.


There are several major brands of rabies vaccines available for dogs in the United States. The most common include Merial’s Imrab 3 and Imrab 3 TF, Boehringer Ingelheim’s Rabvac 3, and Zoetis’ (formerly Pfizer) Defensor 3.

Traditionally, most rabies vaccines contained the preservative thimerosal, which contains mercury. However, in recent years some manufacturers have introduced thimerosal-free versions of their rabies vaccines:

  • Merial offers Imrab 3 TF, a thimerosal-free version of Imrab 3 (Dogsnaturallymagazine.com).
  • Boehringer Ingelheim’s Rabvac 3 is thimerosal-free (Thecheerfulvet.com).
  • Zoetis does not currently offer a thimerosal-free version of Defensor 3.

So there are a couple thimerosal-free options for dog rabies vaccination, primarily from Merial and Boehringer Ingelheim. However the thimerosal-containing versions are still commonly used as well.

Administration and Safety

Like all vaccines, the rabies vaccine should be administered properly and safely. The CDC provides the following guidelines for safe administration of the rabies vaccine https://www.cdc.gov/rabies/medical_care/vaccine.html:

administering rabies vaccine to a dog in its hind leg muscle.

  • For adult dogs, the vaccine should always be given intramuscularly in the hind leg area.
  • For puppies, the vaccine can also be administered in the scruff area.
  • Use a sterile needle and syringe for each injection.
  • Alternate vaccine injection sites for subsequent doses.
  • Observe dogs after vaccination for any potential adverse reactions, which are very rare.
  • Store and handle the vaccine properly according to the manufacturer’s guidelines.

Following these administration and safety guidelines helps ensure dogs receive the full protective benefits of rabies vaccination.


In summary, rabies vaccines are an essential part of keeping dogs healthy and preventing the spread of this deadly virus. While traditional rabies vaccines contained the preservative thimerosal, mercury-free options have become widely available in recent years. Multiple studies have shown mercury-free rabies vaccines to be just as safe and effective as thimerosal-containing versions. With the mercury removed, these new vaccines avoid the potential risks associated with injecting pets with mercury while still protecting them from rabies.

Veterinary associations and public health authorities strongly recommend vaccinating dogs against rabies to save lives. The small increase in cost for mercury-free vaccines is well worth it for the peace of mind and health benefits. Dog owners should consult their vet on the recommended schedule of rabies boosters and which vaccine options make the most sense for their pet. Ensuring dogs receive their rabies shots protects the health of pets, owners, and communities.
a vet and dog owner discussing rabies vaccine options.

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