COVID-19 outbreak in Algeria: A mathematical model to predict the incidence

Introduction: Since December 29, 2019 a pandemic of new novel coronavirus-infected pneumonia named COVID-19 has started from Wuhan, China, has led to 254 996 confirmed cases until midday March 20, 2020. Sporadic cases have been imported worldwide, in Algeria, the first case reported on February 25, 2020 was imported from Italy, and then the epidemic has spread to other parts of the country very quickly with 90 confirmed cases until March 19, 2020. Methods: It is crucial to estimate the cases number growth in the early stages of the outbreak, to this end, we have implemented the Alg-COVID-19 Model which allows to predict the incidence and the reproduction number R0 in the coming months in order to help decision makers. The Alg-COVIS-19 Model initial equation 1, estimates the cases number at t prediction time using two parameters: the reproduction number R0 and the serial interval SI. Results: We found R0=2.56 based on actual incidence at the first 23 days, using the serial interval SI= 4,4 and the prediction time t=23. The herd immunity HI estimated is HI=61%. Also, The Covid-19 incidence predicted with the Alg-COVID-19 Model fits closely the actual incidence during the first 23 days of the epidemic in Algeria Fig. 1.A. which allows us to use it. According to Alg-COVID-19 Model, the number of cases will exceed 5000 on the 40th day ,April 5th, and it will double to 10000 on 43th day of the epidemic, April 8th, thus, exponential phase will begin ,Table 2; Fig.1.B, and increases continuously until reaching a herd immunity of 61% unless serious preventive measures are considered. Discussion: This model is valid only when the majority of the population is vulnerable to COVID-19 infection, however, it can be updated to fit the new parameters values.