Makes me wonder why should it be a quadratic or cubic function? Assuming the virus has just began to spread and there are still no countermeasures in place should it not be like some exponential function xⁿ, where x is average number of people infected by each patient and n is nth round of spread (which would depend on time taken by patient to come in contact with x new targets). I think I should read more on disease modeling. This fit seems interesting, nonetheless. Makes me wonder what are dynamics of the spread.