A fed batch process of production of influenza virus which comprises replicating an influenza virus, in cells of an avian cell line wherein said cell line has been obtained by a method comprising the following steps: A) culturing avian embryonic stem cells in a cell culture medium containing the factors allowing their growth, wherein said factors comprise a. a trophic factor selected from the group consisting of stem cell factor, Insulin Growth Factor 1 (IGF-1), and basic Fibroblast Growth Factor (bFGF), and b. a cytokine whose action is through a receptor which is associated with the gp130 protein, selected from the group consisting of leukemia inhibitory factor, interleukin 11 (IL-11), interleukin 6 (IL-6), interleukin 6 receptor (IL-6R), ciliary neurotrophic factor (CNTF), oncostatin and cardiotrophin and supplemented with animal serum in presence of a feeder layer;, B) passage by modifying the culture medium so as to obtain the withdrawal of said exogenous growth factors and cytokines, of the serum and of the feeder layer; C) establishing adherent or non-adherent cell lines capable of proliferating in the absence of said exogenous growth factors, serum and inactivated feeder layer from said cell culture medium; said process of production of influenza virus comprising the steps of: a) proliferating said cells in a cultivation vessel, in suspension, in a serum-free medium N° 1; b) infecting the cells with said influenza virus when the cell density is of at least 1.5 million cells/ml, preferably of at least 4 million cells/ml; c) shortly before infection, simultaneously to infection, or shortly after infection adding to the cell culture serum-free medium N° 2; and d) further culturing said infected cells in order to allow virus replication; and e) optionally, harvesting said virus, wherein said process comprises the additional step of feeding the cells wherein said feeding step comprises the discontinuous addition of glutamine and/or D-glucose during steps a) to d); and wherein glutamine concentration in the culture medium is maintained between around 1 mM to around 3mM, and D-glucose concentration in the culture medium is maintained between around 1 g/l to 10 g/l. A) culturing avian embryonic stem cells in a cell culture medium containing the factors allowing their growth, wherein said factors comprise a. a trophic factor selected from the group consisting of stem cell factor, Insulin Growth Factor 1 (IGF-1), and basic Fibroblast Growth Factor (bFGF), and b. a cytokine whose action is through a receptor which is associated with the gp130 protein, selected from the group consisting of leukemia inhibitory factor, interleukin 11 (IL-11), interleukin 6 (IL-6), interleukin 6 receptor (IL-6R), ciliary neurotrophic factor (CNTF), oncostatin and cardiotrophin a. a trophic factor selected from the group consisting of stem cell factor, Insulin Growth Factor 1 (IGF-1), and basic Fibroblast Growth Factor (bFGF), and b. a cytokine whose action is through a receptor which is associated with the gp130 protein, selected from the group consisting of leukemia inhibitory factor, interleukin 11 (IL-11), interleukin 6 (IL-6), interleukin 6 receptor (IL-6R), ciliary neurotrophic factor (CNTF), oncostatin and cardiotrophin B) passage by modifying the culture medium so as to obtain the withdrawal of said exogenous growth factors and cytokines, of the serum and of the feeder layer; C) establishing adherent or non-adherent cell lines capable of proliferating in the absence of said exogenous growth factors, serum and inactivated feeder layer from said cell culture medium; a) proliferating said cells in a cultivation vessel, in suspension, in a serum-free medium N° 1; b) infecting the cells with said influenza virus when the cell density is of at least 1.5 million cells/ml, preferably of at least 4 million cells/ml; c) shortly before infection, simultaneously to infection, or shortly after infection adding to the cell culture serum-free medium N° 2; and d) further culturing said infected cells in order to allow virus replication; and e) optionally, harvesting said virus,