Current status of virus-vectored vaccines against pathogens that affect poultry

•Some recombinant viral vectors are able to induce strong immune responses in poultry.•Some vectored vaccines could be effective with a single dose by mass vaccination methods.•Recombinant viral vectors should allow distinguishing vaccinated from infected animals.•The main methodology used for inserting heterologous genes is homologous recombination.•Just few of the viral vector based-vaccines that are reported have become commercially available for poultry. The most effective strategies for the control of disease in poultry are vaccination and biosecurity. Vaccines useful against pathogens affecting poultry must be safe, effective with a single dose, inexpensive, applicable by mass vaccination methods, and able to induce a protective immune response in the presence of maternal antibodies. Viral vector meet some of these characteristics and if the attenuated virus used as vector infects birds, the vaccine will have the advantage of being bivalent. Thus, viral vectors are currently a tool of choice for the development of new poultry vaccines. This review describes the main viruses used as vectors for the delivery and in vivo expression of antigens of poultry pathogens. It also presents the methodologies most frequently used to obtain recombinant viral vectors and summarizes the state-of-the-art related to vectored vaccines in poultry (some of them currently licensed), the pathogens targeted and their antigens, and the ability of these vaccines to induce an effective immune response. Finally, the review discusses the results of a few studies comparing recombinant viral vector vaccines and live-attenuated vaccines in vaccine matching challenges, and mentions strategies and future researches that can help to improve the efficacy of vectored vaccines in poultry birds.