vectored vaccines

1. Vectored Vaccines
Division of Veterinary Biotechnology
IVRI, Izzatnagar, Bareiley U.P.
Shabir Hussain Mir
VMC, M-6504

2. Vectors
Agents that carry selected genes encoding foreign antigens are known as vectors.
Genetically engineered vectors can either be used as vaccines themselves or used
to produce large amounts of antigens in-vitro that can then be incorporated into
vaccines.
Vectors include bacteria, DNA viruses, yeasts, plasmids, and even plants.
 Some microbial vectors may also replicate within an animal and as a result
stimulate protective immune responses, provided they only cause abortive
infections.
The first commercially available vectored vaccine used a fowlpox vector.

3. Viral vector vaccines
Viral vector vaccines use a harmless virus to deliver to the hosts cells the genetic code of the
antigen you want the immune system to fight. “They are basically a gene delivery system,”.
 Experimental recombinant vaccines used as vaccine platforms have usually used large DNA
viruses such as poxviruses, adenoviruses, and herpesviruses ; the organisms that have been most
widely employed for this purpose in veterinary medicine are poxviruses such as vaccinia, fowlpox,
and canarypox.
Poxviruses are the most widely used vectors in vaccines because they have a very large genome
that can accommodate large inserts.
No viral vector vaccine had ever been licensed for full human use before the COVID-19
pandemic.
Benefits: Viral vector vaccines usually trigger a strong immune response. Typically, only one dose
of the shot is needed to develop immunity. Boosters may be needed to maintain immunity.

4. Viral vectored vaccines have the advantage of being able to induce both antibody- and
cell- mediated immune responses without the need for an adjuvant.
They do not require complex purification.
They can generate antigens in the correct conformation and they can deliver more than one antigen
at a time. As a result, these vaccines are safe, they cannot be transmitted by arthropods, and they
are not excreted in body fluids.
Their major advantage is that the antigens are synthesized within infected cells and thus act as
endogenous antigens.
They produce a “balanced” immune response compared to inactivated viral vaccines.
In selecting viral vectors for vaccine use, safety is of paramount importance, whereas other
considerations include vector stability and the ability to scale-up production.

5. The various methods of generating live recombinant vaccines. The
gene encoding the antigen of interest is isolated, inserted into a
plasmid. This plasmid can then be inserted into many different potential
vectors.

6. The production of an oral vaccinia rabies
recombinant vaccine. Vaccinia has been
selected because its genome can
accommodate a very large gene insert. In
addition, the recombinant vaccinia readily
induces protective immunity following oral
vaccination.

8. Viral vector-based vaccines differ from most conventional vaccines in that they don’t actually contain antigens, but
rather use the body’s own cells to produce them. They do this by using a modified virus (the vector) to deliver genetic
code for antigen, in the case of COVID-19 spike proteins found on the surface of the virus, into human cells.

9. By infecting cells and instructing them to make large amounts of antigen, which then trigger an immune response,
the vaccine mimics what happens during natural infection with certain pathogens - especially viruses.

10. This has the advantage of triggering a strong cellular immune response by T cells as well the production of
antibodies by B cells. An example of a viral vector vaccine is the rVSV-ZEBOV vaccine against Ebola.

12.  High efficiency gene transduction
 Highly specific delivery of genes to
target cells
 Induction of both humoral and cell-
mediated immune responses
 Improved efficacy and safety
 Reduced administration dose
 Enable large-scale manufacturing
 Potential targets ranging from
cancers to a vast number of
infectious diseases
Advantages
 Risk of integrating into the host
genome and lead to other diseases
 The presence of pre-existing
immunity against the vector caused
by previous exposure to the virus
and the production of neutralizing
antibodies can reduce vaccine
efficacy
Disadvantages
Advantages and disadvantages of viral vector vaccines

13. Advantages and disadvantages of different vaccine platforms

14. References
• CDC.gov. Understanding Viral Vector Vaccines COVID-19 Vaccines. Available
at: https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/viralvector.html
• Vaccines for Veterinarians by Ian R. Tizard
• Daian e Silva, D.S.d.O.; da Fonseca, F.G. The Rise of Vectored Vaccines: A Legacy of the COVID-
19 Global Crisis. Vaccines 2021, 9, 1101. https://doi.org/10.3390/vaccines9101101