@article{202106.0155,
	doi = {10.20944/preprints202106.0155.v1},
	url = {https://doi.org/10.20944/preprints202106.0155.v1},
	year = 2021,
	month = {June},
	publisher = {Preprints},
	author = {Andrei Khrennikov},
	title = {Covid-19: Why Herd Immunity was not Approached Anywhere? Ultrametric Diffusion Modeling of Virus Spread in Hierarchically Clustered Population},
	journal = {Preprints}
}