The shift towards new cell culture–based flu vaccine production has been dealt a blow as MedImmune of Gaithersburg, Maryland, puts its manufacturing efforts on hold. The AstraZeneca subsidiary took this step after the US Food and Drug Administration (FDA) requested follow-on studies that would substantially increase the cost and time to market beyond what the company expected. In its contract with the Department of Health and Human Services (HHS), MedImmune proposed an efficacy study comparing immune responses in volunteers receiving cell-produced with those receiving egg-produced vaccines, considering them genetically identical, followed by a large safety trial. But the FDA termed cell-grown vaccine a new product, requesting Medimmune conduct a clinical trial during an influenza season, as well as demonstrate efficacy in adults before vaccinating children. The plan “became cumbersome and complicated and did not address significant scientific and medical issues we thought we needed to address to advance this vaccine,” says George Kemble, vice president of vaccine R&D at MedImmune. “I don't think there is any deliberate delay,” says Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, noting the move is due to safety and efficacy data gathering. Jose Romero, member of the FDA vaccine advisory committee, comments in an unofficial capacity, “General FDA concerns include exposing humans to adventitious agents that might be lurking in cell lines or the remote possibility of transmitting an oncogene that could create cancer in a human host.” Elsewhere, last November, Novartis of Basel inaugurated a $1 billion cell culture flu vaccine manufacturing facility in partnership with the HHS. The plant in Holly Springs, North Carolina, is the first large-scale cell culture flu vaccine and adjuvant production facility in the US.