GSK's novel split-virus adjuvanted vaccines for the prevention of the H5N1 strain of avian influenza infection.

Although influenza pandemics occur infrequently, they are unpredictable. Given that humans had not been previously exposed to the novel H5N1 strain, few (if any) individuals have any degree of immunity to the strain. GlaxoSmithKline plc (GSK) has developed two inactivated split H5N1 vaccines adjuvanted with GSK's proprietary oil-in-water emulsion AS03: GSK-1562902A (produced in Dresden, Germany) and GSK-1557484A (produced in Québec, Canada). The vaccines principally use an A/Vietnam strain virus; following the vaccination of influenza-naïve ferrets, potent neutralizing titers against the homologous A/Vietnam strain virus and against a heterologous A/Indonesia strain virus were elicited. In phase I, II and III clinical trials, two administrations of low doses (3.8 microg) of the vaccines induced protective immunity in more than 90% of vaccinees. The vaccines were generally well tolerated; the most frequently reported local adverse event was pain at the injection site. The vaccines, which can be administered in the pre-pandemic and pandemic setting, were approved in Europe in May 2008 as Prepandrix and Pandemrix, respectively. Phase II/III trials were also ongoing at the time of publication for both GSK-1562902A and GSK-1557484A. With the enormous demand for an effective vaccine in the event of an H5N1 pandemic, GSK's inactivated split H5N1 virus vaccine likely will be a highly valued product.