H5N1 Clinical Trials - Current Status of H5N1 Candidate Vaccines

Current Status of H5N1 Candidate Vaccines

Candidate vaccines were developed in the United States and the United Kingdom during 2003 for protection against the strain that was isolated from humans in Hong Kong in February 2003 but the 2003 strain died out in 2004 making the vaccine of little use. In April 2004, WHO made an H5N1 prototype seed strain available to manufacturers. In August 2006, WHO changed the prototype strains and now offers three new prototype strains which represent three of the six subclades of the clade 2 virus which have been responsible for many of the human cases that have occurred since 2005.

The National Institute of Allergy and Infectious Diseases (NIAID) awarded H5N1 vaccine contracts to Aventis Pasteur (now Sanofi Pasteur) of Swiftwater, Pennsylvania, and to Chiron Corporation of Emeryville, California. Each manufacturer is using established techniques in which the virus is grown in eggs and then inactivated and further purified before being formulated into vaccines.

"A universal influenza vaccine could provide protection against all types of influenza and would eliminate the need to develop individual vaccines to specific H and N virus types. Such a vaccine would not need to be reengineered each year and could protect against an emergent pandemic strain. Developing a universal vaccine requires that researchers identify conserved regions of the influenza virus that do not exhibit antigenic variability by strain or over time. A universal vaccine is being developed by the British company Acambis and is being researched by others as well. Acambis announced in early August 2005 that it has had successful results in animal testing. The vaccine focuses on the M2 viral protein, which does not change, rather than the surface hemagglutinin and neuraminidase proteins targeted by traditional flu vaccines. The universal vaccine is made through bacterial fermentation technology, which would greatly speed up the rate of production over that possible with culture in chicken eggs, plus the vaccine could be produced constantly, since its formulation would not change. Still, such a vaccine is years away from full testing, approval, and use." As of July 2007, phase I clinical trials on humans are underway in which a vaccine that focuses on the M2 viral protein "is being administered to a small group of healthy people in order to verify the safety of the product and to provide an initial insight into the vaccine’s effect on the human immune system." (See also Universal flu vaccines)

In June 2006, the National Institutes of Health (NIH) began enrolling participants in a Phase 1 H5N1 study of an intranasal influenza vaccine candidate based on MedImmune's live, attenuated vaccine technology.

Oct 2010 Inovio starts a phase I clinical trial of its H5N1 vaccine (VGX-3400X).