A vaccine composition for birds comprising as an active ingredient a structure containing O-antigen derived from Gram-negative bacteria, provided that said structure does not contain a whole cell, and a process for preparing the same are provided. By using a structure containing O-antigen (e.g. lipopolysaccharide) derived from Gram-negative bacteria as an active ingredient in accordance with the present invention, alleviation of inoculation reaction and reduction in an amount of injection are attained as compared to the conventional whole-cells vaccine to thereby allow for the increase in the number of other antigens to be mixed therewith.

A recombinant vaccine comprising a serotype 9 fowl adenovirus vector (FAdV-9) having at least one exogenous nucleotide sequence inserted encoding at least one antigen of a disease of interest and replacing the adenovirus genome non-essential region, and a pharmaceutically acceptable vehicle, adjuvant and/or excipient, wherein the at least one exogenous nucleotide sequence encoding at least one antigen of a disease of interest and replacing the adenovirus genome non-essential region is located between the 491 and 2782 nucleotides.

The vector of this vaccine is stable for industrial scale production. Likewise, even when administering this vaccine in combination with a vaccine against Marek's disease, both vaccines produce an adequate immune response which is not affected by interference between each other. In the same way, effectiveness of the recombinant vaccine is not affected by maternal antibodies, and is capable of inducing both an early and lasting protective response, even with only one application.

A recombinant vaccine comprising a serotype 9 fowl adenovirus vector (FAdV-9) having at least one exogenous nucleotide sequence inserted encoding at least one antigen of a disease of interest and replacing the adenovirus genome non-essential region, and a pharmaceutically acceptable vehicle, adjuvant and/or excipient, wherein the at least one exogenous nucleotide sequence encoding at least one antigen of a disease of interest and replacing the adenovirus genome non-essential region is located between the 491 and 2782 nucleotides. The vector of this vaccine is stable for industrial scale production. When administering this vaccine in combination with a vaccine against Marek's disease, both vaccines produce an adequate immune response which is not affected by interference between each other. In the same way, effectiveness of the recombinant vaccine is not affected by maternal antibodies, and is capable of inducing both an early and lasting protective response, even with only one application.