Novel means and methods are provided for the production of mammalian viruses, comprising infecting a culture of immortalized human cells with the 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 - human cells of the present invention can be cultured under defined serum free conditions, and the cells show improved capability for propagating virus. In particular, methods are provided for producing in cultured human cells Influenza virus and vaccines derived thereof. This method eliminates the necessity to use whole chicken embryos for the production of Influenza vaccines.; The method provides also for the continuous or batchwise removal of culture media. As such, the present invention allows the large scale continuous production of viruses to a high titer.