COVID-19 multiwaves as multiphase percolation: a general N-sigmoidal equation to model the spread Ahmed El Aferni, Moez Guettari and Abdelkader Hamdouni Eur. Phys. J. Plus, 138 5 (2023) 393 Published online: 08 May 2023 DOI: 10.1140/epjp/s13360-023-04014-0