The probability of human-to-human transmission of H5N1 is “very very low,” Chowdhury says. But if it had been to occur in the sustained manner, it could rock the world in a way not found since the 1918 Spanish Flu. five to 7. For H5N1 amongst birds, it's around a hundred. https://www.dailypioneer.com/2018/state-editions/tac-proposals-a-political-ploy-hemant.html