This article will take a different approach than seen in the other vaccine articles, and focus on a specific recent scholarly study. The study, “Duration of immunity after rabies vaccination in dogs: The Rabies Challenge Fund research study,” by Jean Dodds, Doctor of Veterinary Medicine, is one of the first research pieces aimed to discover the immunity level needed to protect a dog from rabies and how long vaccine immunity is protective. With an increase in the use of titer tests across the veterinary field, many professionals have sought out to determine the factors to create a rabies titer test as well. As discussed in previous core vaccine articles, some vaccinations are shown to hold longer immunity than we first believed, leading to the importance of the titer test, and avoiding over-vaccination.
“While rabies vaccines are highly efficacious, they are also among the most reactogenic of vaccines…research has shown that potent, adjuvanted, killed rabies vaccines elicit the most frequent and severe adverse reactions in animals…”
Titer tests have been developed for vaccines such as parvo and distemper, allowing Veterinarians to determine if a booster is necessary at a certain time. However, it’s been noted that rabies is the only vaccine required by law for domestic animals, and has the least amount of studies in determining the immunity level. The rabies vaccine is also known to be one the most reactive of the vaccines; Meaning they saw the most adverse effects of any canine vaccine with the rabies. While titer tests are typically used for revaccination purposes it can also be used to identify if your dog has any immunity compromising issues. Thankfully UC Davis and Penn State Veterinary Schools have developed accurate titer tests to determine antibody levels against the disease in dogs. If you’d like to learn about your dog’s specific immunity against rabies a blood sample can be sent to either of these Universities for analysis. We hope these tests become more widely available and used by all members of the community.
“A yearly rabies titer would more effectively assess a pet’s level of protection from unknown rabies virus exposures than the current practice of relying on mandated rabies immunization intervals, for which there is no documentation of immune response, or lack thereof in the case of a non-responder or vaccine failure.”
The study by Dodds and the team was performed with an available rabies vaccine that is free of the preservative thimerosal to avoid adverse effects from outside components. Although, unlike vaccines on the market, they also used a live product vaccine. The data suggested that rabies vaccines create an immunity for well beyond three years and to continuing to excessive vaccination beyond that could lead to harmful results. From this study alone, doctors are challenging the idea that the rabies vaccine provides limited immunity, instead point a general time period of protection at around 6 years. They also determined a range as to where immunity will no longer protect your pup against rabies – above 0.5 IU/mL. When an animal falls close, or below that level, is when it is recommended to administer a booster vaccine. There are two charts from this study which show the immunity time of a rabies vaccine, as well as, the immunity levels depending on previous vaccinations.
Image 1: Shows the rate of survival for each group when exposed to the rabies virus after a certain period of time. The controlled group was never vaccinated, and the following three time groups were: 6 years 7 Months, 7 years 1 Month and 8 years.
From the image above, doctors studying the duration of immunity after rabies vaccines determined that no-vaccination or immunity below 0.5 IU/mL would not survive if exposed to the rabies virus. Out of the five subjects exposed to rabies, six years and seven months after their vaccine, 80 percent survived. The remaining subjects in the group, seven years and one month since their last vaccine, 50 percent of the dogs exposed to rabies lived. Once exposed for eight years after the vaccine, they saw an 80 percent mortality rate. From this we can see that the immunity begins to decrease heavily after six years, leaving the animals more exposed.
The data suggests a four to five year recommendation is appropriate and needed to examine this inflection point on a broader level. It highlights the need to re-examine rabies vaccination laws and shows there is absolutely no justification for towns or states to mandate yearly rabies boosters. We are harming our dogs in doing so with no benefit regarding immunity. Community advocacy is needed to make a change, it won’t happen without involvement from the public and we hope to get our audience interested in this issue as well to ensure healthy pets everywhere.
Image 2: Shows the second part of the trial focuses on the efficiency of two types of boosters, one killed, one recombinant[DNA antigen] and the levels of immunity observed. The study was a 14 days cycle in which four groups of dogs A-D. [A: previously vaccinated, boosted with killed, B: previously vaccinated, boosted with recombinant. C: No vaccines, boosted with killed. D: No vaccines, boosted with recombinant.]
The results show that dogs who were previously vaccinated, groups A and B both showed higher levels of immunity than groups C and D after receiving a booster. However, Group B, who was previously vaccinated and received the recombinant booster had nearly four times more immunity than group A, who was previously vaccinated but boosted with a killed vaccine. For groups C and D, they both came up short to having enough immunity to protect a dog from rabies.
Overall, this study went beyond its goal of determining an immunity level by challenging different types of boosters and concentrations of the vaccine related to immunity. It’s important to not only determine the immunity time but also the importance of getting your dog vaccinated as a pup. The controlled group, dogs with no vaccines, proving if they are faced with rabies, they will not beat it. Beyond that it also shows why we as owners are the best representation our dogs get. It is important that not only our Veterinarians are up to date with best practices and advocate for improved policies, but that you are too!
