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The one known subclade of H5 is H5a, defined by T4336C in the control region, which has its own subclades of H5a1 and H5a2.[3] H5a is thought to be around 7000–8000 years old, in other words, the mutation T4336C probably occurred c. 5500 BC. It is fairly evenly distributed at low levels across Europe. The average in samples from Austria, Germany, Hungary, Macedonia , and Romania was 2.4%.[9] Yet it is almost absent from the Caucasus and the Near East, suggesting a European origin.
Álvarez-Iglesias et al. observed a frequency peak for H5a in the Franco-Cantabrian region decreasing towards East Europe and commented that "This is compatible with a process of demographic repopulation of Europe after the LGM period centered in this climatic and geographic refuge."