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What makes for a successful oral rabies vaccination programme?

Oral rabies vaccination (ORV) programmes differ in approach and scale depending upon the species being targeted. In Europe, foxes and raccoon dogs are the main reservoir and are the focus of sustained vaccination programmes over the last 30 years. In Asia and Africa, the presence of free-roaming dogs inaccessible for vaccination by the parenteral route forms a serious obstacle for programmes to eradicate human deaths from dog-mediated rabies by 2030.

A successful ORV programme relies on three core components: the vaccine, an attractive bait and the distribution system used to target the animal in question.

Vaccines

New Ceva third generation vaccines – safety engineered, by design

As all oral rabies vaccines are based on replication-competent live viruses there is a potential safety risk when dogs or other non-target species, including humans, come in direct or indirect contact with the vaccine virus. 

For example, a low residual pathogenicity was observed with first generation oral rabies virus vaccines. To develop safer vaccines, research indentified changes that could be made to the G-protein to abolish residual pathogenicity. Subsequently, additional changes were made to reduce reversion to virulence in these vaccine candidates.

The result? A new third generation vaccine, safer by design – the new gold standard for 21st century oral rabies vaccination programmes.

 

History of first and second generation vaccines

The history of the development of the concept of oral vaccination against rabies and the development of the first vaccine candidates is fascinating. All vaccines used for oral rabies vaccination (ORV) programmes are based on live replication-competent viruses.

  • First developed in 1970’s
  • Developed through in-vivo and in-vitro serial passaging, leading to various vaccines (SAD Bern or SAD19 for example)

Some later developments lead to so-called second generation vaccines by selection of monoclonal antibody mutants.

 

Bait design

To be successful, baits must be attractive to the target species and be able to deliver the vaccine efficiently

  • Often attractants, e.g. baits, used for one species are not attractive for another species, so species-specific baits are required
  • Regional differences in food preference should be considered

 

The vaccine is delivered from sachets within the bait

  • Timely release into the oral cavity is imperative
  • Baits should be designed to be chewed and not swallowed whole
  • Bait design should help avoid excessive spillage of the vaccine

 

Distribution

Hand-out distribution model for free-roaming dogs

As dogs and humans co-exist within the same environment, the vaccination of free-roaming dogs can not be carried out in the same way as for wild animals:

  • Parenteral vaccination programmes are the basis for elimination
  • But not all dogs can be vaccinated in this way
  • ORV is employed as a complementary tool

Free-roaming dogs share their habitat with humans, which makes aerial distribution inappropriate:

  • Vaccines are based on live viruses
  • Although highly attenuated and safe, human contact with the virus should be avoided
  • According to WHO and OIE for ORV of free-roaming dogs, the handout and retrieve model should be used
  • Baits not taken by dogs are retrieved
  • Discarded sachets post bait consumption are collected
  • Potential human contact with the vaccine is limited

Aerial distribution for foxes and raccoon dogs

Working with experts, IDT has developed a satellite-navigated, computer-supported, fully-automated system for aerial distribution of vaccine baits from the air (SURVIS) into unpopulated areas where the target animal lives.

  • Optimised precision drops via GPS results in higher immunisation rates
  • Each bait is tracked with location, time and release date
  • Allow for evaluation and optimisation of programme
  • The cost-effective gold standard solution