means and methods for producing mammalian viruses , the method comprising infecting a culture of immortalized human cells with a virus , incubating the culture infected with virus to propagate the virus under conditions that permit growth of the virus , and to form a virus - containing medium , and removing the virus - containing medium . the viruses can be harvested and be used for the production of vaccines . advantages include that human cells of the present invention can be cultured under defined serum - free conditions and the cells show improved capability for propagating virus . methods are provided for producing , in cultured human cells , influenza virus and vaccines derived thereof . this method eliminates the necessity of using whole chicken embryos for the production of influenza vaccines . the method also provides for the continuous or batch - wise removal of culture media . as such , the present invention allows the large - scale continuous production of viruses to a high titer .