A non-autonomous time-delayed SIR model for COVID-19 epidemics prediction in China during the transmission of Omicron variant

With the continuous evolution of the coronavirus, the Omicron variant has gradually replaced the Delta variant as the prevalent strain. Their inducing epidemics last longer, have a higher number of asymptomatic cases, and are more serious. In this article, we proposed a nonautonomous time-delayed susceptible-infected-removed (NATD-SIR) model to predict them in different regions of China. We obtained the maximum and its time of current infected persons, the final size, and the end time of COVID-19 epidemics from January 2022 in China. The method of the fifth-order moving average was used to preprocess the time series of the numbers of current infected and removed cases to obtain more accurate parameter estimations. We found that usually the transmission rate $\beta (t)$ was a piecewise exponential decay function, but due to multiple bounces in Shanghai City, $\beta (t)$ was approximately a piecewise quadratic function. In most regions, the removed rate $\gamma (t)$ was approximately equal to a piecewise linear increasing function of (a*t+b)*H(t-k), but in a few areas, $\gamma (t)$ displayed an exponential increasing trend. For cases where the removed rate cannot be obtained, we proposed a method for setting the removed rate, which has a good approximation. Using the numerical solution, we obtained the prediction results of the epidemics. By analyzing those important indicators of COVID-19, we provided valuable suggestions for epidemic prevention and control and the resumption of work and production.