Skip to McMaster Navigation Skip to Site Navigation Skip to main content
McMaster logo

Institute on Ethics & Policy for Innovation

Transmissible Vaccines

Transmissible vaccination is a type of inoculation that targets wild animals and can spread between hosts autonomously, with the goal of preventing transmission of animal pathogens to human populations. The development of transmissible vaccines is a promising innovation, particularly due to the challenges of conducting large-scale vaccination campaigns that target wild animals. As an emerging technology enabled by genetic engineering, transmissible vaccines have the potential to revolutionize vaccination and infectious disease control. Examples of successful transmissible vaccines include cytomegalovirus-based (CTV) vaccines against myxoma virus and rabbit hemorrhagic disease virus among wild rabbits, and Sin Nombre virus among deer mice populations. Currently, a transmissible vaccine that protects apes and fruit bats against Ebola is under development.

Expandable List

What are Transmissible Vaccines?

The transmissible vaccines that have been developed in recent decades aim to prevent zoonotic pathogens in animal reservoirs from spilling over into human populations.6 Due to the difficulties of conducting large-scale vaccination campaigns that target wild animals, the development of transmissible vaccines is a promising innovation with the potential to reach wildlife populations more effectively.7

“Self-disseminating” or autonomous vaccines are classified into:

  • transmissible vaccines, which are live viral vaccines with the ability to transmit between hosts; and
  • transferable vaccines, which are administered on the skin or fur of an animal, and then transferred to other animals through grooming behaviours.1

As opposed to traditional viral vaccines, which rely on individual-based direct vaccination, transmissible vaccines can transmit between vaccinated individuals and their contacts, referred to as “chains of transmission,” in the same way that viruses are caught and spread.2 They are benign, yet infectious, typically at a lower rate than disease-causing viruses.

How Do Transmissible Vaccines Work?

Transmissible vaccines represent an emerging technology bolstered by rapid advances in the genetic engineering of live viral vaccines.1 There are two mechanisms used for the design of transmissible vaccines. The first mechanism is an attenuated vaccine, which requires weakening a virus and transforming it into a benign vaccine. The second method is a recombinant transmissible vaccine (RTV), which requires combining a benign vector virus with the antigenic genes of a target pathogen.3

Employing a transmissible vaccine requires the introduction of the vaccine to a limited portion of the animal population, which would subsequently transmit the vaccine to new hosts through normal social behaviour. Research indicates that, in real-life conditions, weakly transmissible RTVs represent the most viable and safe option for the inoculation of a population.4 While a transmissible vaccine would not spread indefinitely, and levels of transmission would reduce with each host, its impact would theoretically contribute to the achievement of herd immunity within a population.5

Current Applications of Transmissible Vaccines

Transmissible vaccines have the potential to revolutionize vaccination and infectious disease control. Examples of successful transmissible vaccines includes the implementation of an RTV against myxoma virus and rabbit hemorrhagic disease virus among populations of wild rabbits.8 Similarly, a CTV transmissible vaccine has been successfully employed to interrupt the transmission of Sin Nombre virus among deer mice populations.5 Lastly, a CTV transmissible vaccine to control Ebola within wildlife reservoirs, targeting primarily apes and fruit bats, is currently under development.

Risks and Challenges of Transmissible Vaccines

  • While the safest types of transmissible inoculation would require the engineering of a weakly transmissible vaccine that could reduce transmission chains and ensure extinction, a weak inoculation would limit the ability of the vaccine to reach subpopulations.3
  • An important risk associated with live-attenuated transmissible vaccines is the potential for an evolutionary reversion of the virus to a high or wild-type virulence that could lead to an increasing number of outbreaks.4

Another important risk is the potential for a vaccinated host to have a persistent infection, as seen with immunocompromised hosts, that could transmit the virus to a greater extent and potentially allow it to incubate for a long period of time, causing a long-term evolution within the host.9

The performance of transmissible vaccines under real-world conditions is largely unknown. A major research limitation is the fact that modeling studies often assume host homogeneity.1 Under real-life conditions, host heterogeneity, including how long a host remains immune and the nature of cross-immunity, greatly influences the outcome of vaccination campaigns. Host heterogeneity often results in the need for greater vaccination rates than would be required for a uniform population.11 Researchers might benefit from developing and testing transmissible vaccines among well-understood systems that facilitate the management of risks, and thereby enable a better understanding of the evolutionary epidemiology that occurs through the use of these tools.2

  1. Varrelman TJ, Basinski AJ, Remien CH, Nuismer SL. Transmissible vaccines in heterogeneous populations: Implications for vaccine design. One Health [Internet]. 2019 Jun 1;7:100084. Available from: https://www.sciencedirect.com/science/article/pii/S2352771418300454
  2. Nuismer SL, Bull JJ. Self-disseminating vaccines to suppress zoonoses. Nature Ecology & Evolution [Internet]. 2020 Sep [cited 2020 Sep 4];4(9):1168–73. Available from: https://www.nature.com/articles/s41559-020-1254-y
  3. Bull JJ, Smithson MW, Nuismer SL. Transmissible Viral Vaccines. Trends Microbiol [Internet]. 2018 Jan [cited 2019 May 3];26(1):6–15. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5777272/
  4. Nuismer SL, Althouse BM, May R, Bull JJ, Stromberg SP, Antia R. Eradicating infectious disease using weakly transmissible vaccines. Proceedings of the Royal Society B: Biological Sciences [Internet]. 2016 Oct 26 [cited 2019 May 2];283(1841):20161903. Available from: https://royalsocietypublishing.org/doi/full/10.1098/rspb.2016.1903
  5. Murphy AA, Redwood AJ, Jarvis MA. Self-disseminating vaccines for emerging infectious diseases. Expert Rev Vaccines [Internet]. 2016 Jan 2 [cited 2019 May 6];15(1):31–9. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4732410/
  6. Smithson MW, Basinki AJ, Nuismer SL, Bull JJ. Transmissible vaccines whose dissemination rates vary through time, with applications to wildlife. Vaccine [Internet]. 2019 Feb 21 [cited 2019 May 8];37(9):1153–9. Available from: http://www.sciencedirect.com/science/article/pii/S0264410X19300726
  7. Nuismer SL, Basinski A, Bull JJ. Evolution and containment of transmissible recombinant vector vaccines. Evolutionary Applications [Internet]. 2019 [cited 2020 Sep 4];12(8):1595–609. Available from: http://onlinelibrary.wiley.com/doi/abs/10.1111/eva.12806
  8. Bárcena J, Morales M, Vázquez B, Boga JA, Parra F, Lucientes J, et al. Horizontal Transmissible Protection against Myxomatosis and Rabbit Hemorrhagic Disease by Using a Recombinant Myxoma Virus. J Virol [Internet]. 2000 Feb [cited 2021 Oct 20];74(3):1114–23. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC111445/
  9. Bull JJ. Evolutionary reversion of live viral vaccines: Can genetic engineering subdue it? Virus Evol [Internet]. 2015 Jul 31 [cited 2019 May 12];1(1). Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4811365/
  10. Nuismer SL, May R, Basinski A, Remien CH. Controlling epidemics with transmissible vaccines. PLoS One [Internet]. 2018 May 10 [cited 2019 May 8];13(5). Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5945036/

October 2021