This document provides guidance to national regulatory authorities and vaccine manufacturers on the safe production and quality control of human influenza vaccines produced in response to a threatened pandemic. The document details international biosafety expectations for both pilot-scale and large-scale vaccine production and control and is thus relevant to both development and production activities. It should be read in conjunction with the WHO Laboratory Biosafety Manual (1) and replaces the earlier WHO guidance Production of pilot lots of inactivated influenza vaccines from reassortants derived from avian influenza viruses: Interim biosafety risk assessment (2). Tests required to evaluate the safety of candidate influenza vaccine reference viruses by WHO Reference Laboratories prior to release to vaccine manufacturers are also specified in this document. The following text is written in the form of guidelines rather than recommendations. Guidelines allow greater flexibility than recommendations with respect to expected future developments in the field. These guidelines specify steps to minimize the risk of introducing influenza virus strains with pandemic potential from a vaccine manufacturing facility into the community. If a national regulatory authority so desires, these guidelines may be adopted as definitive national requirements, or modifications may be justified and made by a national regulatory authority. It is recommended that modifications to the principles and technical specifications of these guidelines be made only on condition that the modifications ensure that the risks of introducing influenza virus to the community are no greater than as outlined in the guidelines set out below. © World Health Organization.