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What is a Viral Vector Vaccine?

A vaccine that employs a viral vector to transfer genetic material coding for the desired antigen into the recipient’s host cells is known as a viral vector vaccine. Six viral vector vaccines have been approved in at least one nation as of April 2021: four COVID-19 vaccines and two Ebola vaccines. A modified form of one virus is used as a vector to deliver a nucleic acid coding for an antigen for another infectious agent to a cell. Neither the virus employed as the vector nor the source of the antigen is infected by viral vector vaccines. It does not integrate the genetic material it gives into a person’s DNA.

Unlike subunit vaccinations, which solely provide humoral immunity, viral vector vaccines enable antigen expression within cells and produce a strong cytotoxic T cell response. Because the essential genes are deleted, most viral vectors are engineered to be incapable of replication.

COVID-19 Virus Vector Vaccine

The genetic material from the COVID-19 virus is put in a modified form of a different virus in this sort of vaccination (viral vector). When the viral vector enters your cells, it transmits COVID-19 virus genetic information that instructs your cells to manufacture copies of the S protein. Your immune system responds by producing antibodies and protective white blood cells when your cells exhibit the S proteins on their surfaces. If you are infected with the COVID-19 virus later, the antibodies will help you fight it.

You can’t get infected with the COVID-19 virus or the viral vector virus if you get a viral vector vaccination. Furthermore, the given genetic material does not become a part of your DNA. The COVID-19 vaccine from Janssen/Johnson & Johnson is a vector vaccine. A vector COVID-19 vaccine is also available from AstraZeneca and the University of Oxford.

COVISHIELD

It was developed by Oxford University and AstraZeneca. It is administered by intramuscular injection and uses the modified chimpanzee adenovirus ChAdOx1 as a vector. The Oxford–AstraZeneca COVID-19 vaccine is a replication-deficient simian adenovirus vector that contains the full-length codon-optimized coding sequence of the SARS-CoV-2 spike protein as well as a tissue plasminogen activator (tPA) leader sequence. Because parts of the adenovirus’s critical genes were deleted and replaced with a spike protein-coding gene, the adenovirus is referred to be replication-deficient. Following immunization, the adenovirus vector penetrates the cells and releases its genes, which are carried to the nucleus, where they are then translated into proteins by the cell’s machinery.

Ebola Vector Vaccines

NewLink Genetics of Ames, Iowa, has a license for an Ebola vaccine that was initially developed by the Public Health Agency of Canada, which retains intellectual property rights to it. An attenuated vesicular stomatitis virus, like rabies virus, provides the vector for this monovalent Ebola Zaire vaccine. Humans can be infected with the vesicular stomatitis virus (VSV), although this is a self-limiting illness. Although a safe VSV vaccination for animals has been produced, it is currently unavailable in the United States.

A vaccine candidate developed at Thomas Jefferson University’s Vaccine Center may be ready for human testing. This vaccine, created by Jefferson’s Matthias Schnell, uses an inactivated rabies virus vector to deliver Ebola antigens. Macaques have been given versions of the vaccine that contain both Ebola Zaire and Ebola Sudan antigens as well as Marburg virus antigens. The National Institute of Allergy and Infectious Diseases and the Department of Defense provided funding for the development of a clinical lot of the vaccine for a possible Phase 1 study.

Johnson & Johnson is working on a prime-boost Ebola vaccine. This two-step method begins with direct DNA exposure (the “prime”), followed by the administration of the same or a comparable antigen in a virus that does not reproduce effectively in human tissue (the “boost”). This method has been demonstrated to produce a strong immunological response to the antigen of interest in several situations. The Phase 1 study will begin in the United States and Europe in January 2015. The boost vaccination is based on a recombinant adenovirus vector that delivers an Ebola Zaire surface protein, while the first dose employs a DNA vaccine to prepare the immune system to create Ebola Zaire and Ebola Sudan surface proteins.

Sources and references: https://www.historyofvaccines.org/content/articles/ebola-virus-disease-and-ebola-vaccines

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