Vector vaccines are genetically engineered vaccines in which a gene from one organism, the donor, is inserted into the genome of another organism, the vector, to elicit a protective immune response against both organisms. The donor organism provides a gene that translates to a key protective antigen and the vector organism is a virus or bacterium, the genome of which contains a region that is not required for replication, i.e. a non-essential region.

Dr Kristi Moore

Currently in the United States, two poultry vectors have been approved for use in vector vaccines; they are fowl pox virus (FPV) and herpesvirus of turkeys (HVT).

The first and foremost reason for using a vectored vaccine is safety. Some live vaccines used in the poultry industry have less than desirable side-effects, such as horizontal transmission, vertical transmission, reversion to virulence and vaccine reactions, any of which may result in disease or production loss. With a vector vaccine, the donor gene is inserted into a 'safe' vaccine vector, thus separating the key protective antigen from the live donor organism and its undesirable side-effects.

Since the gene, known as protective, is removed from the donor organism and is inserted into a vector, the characteristics of the donor organism are no longer a factor, while the characteristics of the vector become more important. If vaccine administration occurs early in the life of a chick, then the presence of maternal antibody plays a major role in vaccine efficacy.

To by-pass the interference of these maternal antibodies, MD cell-associated vaccines are used.

Using a cell-associated, HVT-vectored vaccine, protection against Marek's disease is not compromised and, amazingly, the protection elicited by the expressed gene-insert, such as the VP2 gene from IBDV, is not adversely affected in the presence of high levels of specific maternal antibody.

Ceva has a well established line of 13 vectored vaccines using FPV and HVT as vectors for infectious laryngotracheitis virus, infectious bursal disease virus, Newcastle disease virus, Mycoplasma gallisepticum and avian influenza virus. The safety (animal, public health and environmental) and the efficacy have been approved by USDA APHIS CVB. In addition, Ceva's scientists have documented the safety and efficacy of our vectored vaccines.

Scientists have learned a great deal about the advantages and limitations of vector vaccines since their first introduction in 1994. The fast moving pace of biotechnology has allowed us at Ceva to overcome these limitations and provide excellent disease prevention tools for the poultry industry. By mastering the science of vector vaccine technology, we provide you with a line of 13 USDA-licensed vectored vaccines with two more currently in the licensing process.

Further Reading

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You can view other papers presented at the Vector Vaccines Symposium by clicking here.

Further Reading

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Find out more information on the diseases mentioned in this article by clicking here.