The hemagglutinin sequences of most of the H5N1 avian influenza viruses circulating in the past few years fall into two genetic groups, or clades. Clade 1 includes human and bird isolates from Vietnam, Thailand, and Cambodia and bird isolates from Laos and Malaysia. Clade 2 viruses were first identified in bird isolates from China, Indonesia, Japan, and South Korea before spreading westward to the Middle East, Europe, and Africa. The clade 2 viruses have been primarily responsible for human H5N1 infections that have occurred during late 2005 and 2006, according to WHO. Genetic analysis has identified six subclades of clade 2, three of which have a distinct geographic distribution and have been implicated in human infections:

Subclade 1, Indonesia
Subclade 2, Middle East, Europe, and Africa
Subclade 3, ChinaOn the basis of the three subclades, the WHO is offering companies and other groups that are interested in pandemic vaccine development these three new prototype strains:

An A/Indonesia/2/2005-like virus
An A/Bar headed goose/Quinghai/1A/2005-like virus
An A/Anhui/1/2005-like virus[...] Until now, researchers have been working on prepandemic vaccines for H5N1 viruses in clade 1. In March, the first clinical trial of a U.S. vaccine for H5N1 showed modest results. In May, French researchers showed somewhat better results in a clinical trial of an H5N1 vaccine that included an adjuvant. Vaccine experts arent sure if a vaccine effective against known H5N1 viral strains would be effective against future strains.
Although the new viruses will now be available for vaccine research, WHO said clinical trials using the clade 1 viruses should continue as an essential step in pandemic preparedness, because the trials yield useful information on priming, cross-reactivity, and cross-protection by vaccine viruses from different clades and subclades. "</ref>As of November 2006, the United States Department of Health and Human Services (HHS) had enough H5N1 pre-pandemic vaccine to treat about 3 million people (5.9 million full-potency doses) in spite of 0.2 million doses used for research and 1.4 million doses that have begun to lose potency (from the original 7.5 million full-potency doses purchased from Sanofi Pasteur and Chiron Corp.). The expected shelf life of seasonal flu vaccine is about a year so the fact that most of the H5N1 pre-pandemic stockpile is still good after about two years is considered encouraging. Clinical trials
H5N1 clinical trials are clinical trials concerning H5N1 vaccines. They are intended to discover pharmacological effects and identify any adverse reactions the vaccines may achieve in humans. References
Further reading
Khurana S, Suguitan AL, Rivera Y, Simmons CP, Lanzavecchia A, Sallusto F, Manischewitz J, King LR, Subbarao K, Golding H (April 2009). "Antigenic fingerprinting of H5N1 avian influenza using convalescent sera and monoclonal antibodies reveals potential vaccine and diagnostic targets". PLOS Med. 6 (4): e1000049. doi:10.1371/journal.pmed.1000049. PMC 2661249. PMID 19381279. External links
"Diagnostic Targets and Potential Vaccine Against H5n1 Avian Influenza". U.S. Food and Drug Administration (FDA). 2019-10-21. US patent 8778847, "Immunogenic peptides of influenza virus", published 2010-11-11, issued 2014-06-25 
"Pandemic Influenza". HHS.gov. 2016-07-14.