GlaxoSmithKline is developing Daronrix®, a “mock-up” pandemic influenza vaccine for the prophylaxis of influenza infection. The vaccine candidate, an inactivated whole-virion H5N1 vaccine formulated with an alum salt adjuvant, is intended for use once a pandemic has officially been declared by the WHO/E.U. and would be modified to include the exact pandemic strain, once such a strain has been identified. The vaccine has been filed for approval in the E.U. In December 2006, a positive opinion was received in the E.U. for the treatment of influenza.

Daronrix® represents a first step in the preparation against a possible H5N1 pandemic. The benefit of this vaccine, according to the Committee for Medicinal Products for Human Use summary of positive opinion, “can mount an appropriate immune response in individuals that are immunologically naïve against the mock-up virus strain.” The submission dossier was based on a series of data, including a pivotal clinical trial involving 400 healthy adults that evaluated the safety, reactogenicity and immunogenicity of different doses of the candidate vaccine and compared it to different doses of nonadjuvanted H5N1 influenza vaccine. It was concluded from the study, that two doses containing at least 15 mg of H5N1 HA antigen are required to meet the European Medicines Agency (EMEA)'s licensing criteria for seroprotection rate (SP(3)70%), seroconversion rate (SC(3)40%) and seroconversion factor (2.5). The vaccine also had a safety and reactogenicity profile similar to non-adjuvanted vaccine.

GSK has also submitted a second file to the European regulatory authorities for its second-generation H5N1 candidate vaccine. Upon licensure, this second vaccine could potentially be used as part of a proactive pre-pandemic vaccination campaign in advance of a pandemic and give broad protection against different H5N1 strains. This new-generation vaccine candidate could also be adapted for use as a pandemic vaccine once the flu strain causing the pandemic has been identified. Other companies known to be working on potential pandemic influenza vaccines (according to Integrity®) include Novartis, whose MF59-adjuvanted H5N1 vaccine is also under review in the E.U.; as well as Baxter, CSL, Crucell, sanofi pasteur, Generex, Sinovac, PowderMed, MedImmune and the National Institute of Allergy and Infectious Diseases (NIH), each of which has a proprietary H5N1 pandemic influenza vaccine in early clinical testing.