The probability of human-to-human transmission of H5N1 is “incredibly small,” Chowdhury states. However, if it were to happen in a sustained method, it could rock the world in a way not seen since the 1918 Spanish Flu. Hemagglutinin inhibition (HI) assay: The HI assay tests for antibodies towards the hemagglutinin https://www.dailypioneer.com/2014/sports/kumar-sang-a-song.html