Table 1.

Known viral vectors used in vaccine development.

Virus Type	Retrovirus and Lentivirus	Adenovirus	Poxvirus	Alphavirus	Arenavirus	Herpesvirus	Flavivirus	Paramyxovirus	Rhabdovirus
Forms in development	Replication-defective Integrase-defective Single-cycle	Replication-competent Replication-defective	Replication-defective Replication-competent	Replication-competent Replication-defective Single-cycleReplicon	Reverse genetics system Replication-competent	Replication-defective Single-cycle	Replication-competent	Reverse genetics system Replication-competent	Replication-competent Single-cycle
Commonly used vectors	Moloney murine leukemia virus vector	RD-Ad5 SC-Ad6	Modified vaccinia virus Ankara Fowlpox Canarypox	Sindbis virus (SIN) Semliki Forest virus (SFV) Venezuelan equine encephalitis (VEE)	Lymphocytic choriomeningitis virus Pichinde virus	Cytomegalovirus Turkey herpesvirus	YF-17D Yellow fever virus 17D (YF-17D)	Avian paramyxovirus serotype (APMV)-1 APMV-3	Vesicular stomatitis virus (VSV) Rabies
Main advantages	Large packaging capacity Integrating ability Transducing non-dividing cells Ability to be pseudotyped	Broad tropism Variety of systemsdeveloped and tested Strong gene expression	Large packaging capacity Ability to induce a strong cellular immune response Broad host range	Broad tropism Ability to produce a large amount of heterologous protein while maintaining high titers	Low seroprevalence Ability to induce low antiviral immunity Targeting and infection of antigen presenting cells	Large packaging ability Capable of superinfecting a host Induces a long-lived T cell response Ease of manipulation	Ability to induce strong and long lasting adaptive immune response Relatively broad tropism	Does not undergo recombination so the vector is genetically stable Broad tropism Replication is generally limited to the respiratory tract	Ability to induce a robust humoral immune response Lack of preexisting immunity in generalpopulation Ability to be pseudotyped
Disadvantages	Concerns over insertional mutagenesis	Preexisting immunity to human adenoviral species like Ad5	Inability to induce strong immune responses in clinical trials	Transient gene expression so not useful for diseases that require long-term therapeutics	Needs further testing to ensure safety in humans	Causes lifelong infections in hosts so needs to be attenuated	Low immunogenicity of recombinant vectors and vector instability	Needs further testing to ensure safety in humans	Potential of neuro-virulence for rabies virus vector
Insert capacity	8 kB	8 kB	>25 kB	18 kB	4 kB	>30 kB	6 kB	4.5 kB	6 kB
References	[7,8,9]	[10,11,12,13,14]	[15,16,17,18]	[19,20]	[21,22,23]	[24,25,26,27]	[28,29]	[30,31]	[32,33,34,35]