Sigmoid models for Covid-19 pandemic

Several static models for description of the Covid-19 pandemic are considered, analyzed and compared. The best models relative to this pandemic (generalized fractional-power model and generalized inverse tangent model) are new. These and other non-symmetric models are user friendly and show a good agreement with the official data for the pandemic in Europe. The best models give less than 1% error for a 20-day prediction period and less than 1.5% error for a 40-day prediction period. Recommendations for the use of the models are made. The results obtained may be used in the analysis of possible new waves of Covid-19 in different countries, in Europe and worldwide. Such waves seem more and more likely.