An inspection of its facilities in the UK by US regulators is unlikely to delay production of MedImmune’s FluMist vaccine ahead of the upcoming 2007-2008 flu season.

The US Food and Drug Administration has posted details of a warning letter it sent to MedImmune, which is in the process of being acquired by drugs major AstraZeneca, following a visit to the company’s plant in Liverpool where bulk material for FluMist is made. In it, the agency has listed a number of “serious deviations from current good manufacturing practice”, and points out that the Maryland-based firm did not properly investigate when bioburden, or bacteria, found in material eventually used to make FluMist exceeded prespecified limits.

The FDA went on to explain that the early steps of influenza vaccine manufacture involve growing the viruses in hen’s eggs. These early steps in the manufacturing process are not sterile, and therefore some bioburden is expected in the viral harvests obtained from the eggs but this needs to be monitored to ensure the manufacturing process is in control. The agency added that although the viral harvests exceeded the bioburden action limits in some instances at MedImmune in 2006-2007, “all of the filtered monovalent lots and the final trivalent vaccine product met all specifications, including sterility”.

FluMist is currently approved for immunisation of healthy children and adolescents from five to 17 and healthy adults aged 18 to 49, and at this time, the deficiencies noted during the FDA inspection “are not expected to significantly affect the availability of FluMist for the 2007-2008 flu season,” said the agency, “but we will review the progress made by the company on a regular basis”. However, the warning letter is delaying FDA approval of FluMist for use in children younger than five until the problems are closer to resolution.

Linda Peters, senior vice president of regulatory affairs at MedImmune, said “we take the agency's observations with respect to compliance at our bulk manufacturing plant very seriously and are working to promptly and thoroughly respond to its concerns". The company added that the FDA's action will have no impact on the AstraZeneca purchase which is due to close around June 15.