As of March 16, 2020, global confirmed cases of COVID-19 passed 170,568 and has spread to more than 152 countries. As this coronavirus passes into a pandemic, 1 a number of questions arise among the public and government and business leaders: How many cases will there be worldwide? How many deaths can we expect? When will we see a peak in the number of cases?
When will this pandemic end? And, how will recommended immediate actions slow the spread?
A number of the statistical and dynamic models of the Covid-19 outbreak have been applied to analyze its transmission dynamics. [2] [3] [4] [5] [6] [7] [8] These epidemiological models are useful for estimating the dynamics of transmission, targeting resources and evaluating the impact of intervention strategies, but the models require values for unknown parameters and depend on many assumptions, [8] [9] [10] leading to low accuracy and unsure prediction.
To overcome these limitations, we developed a modified auto-encoder (MAE) (eFigure 1), 11 an AI based method for real time forecasting of the new and cumulative confirmed cases of Covid-19 under various interventions around the world. [12] [13] Transfer learning was used to train the MAE. 13 Weights between 0 and 1 were assigned to an intervention variable for the different degrees of interventionszero being no intervention and one being complete. Complete intervention included keeping social distance, washing hands, strict travel restriction, no large group gatherings, mandatory quarantine, restricted public transportation, keep social distance, school closing and closure of all non-essential business, including manufacturing. Using real data to evaluate the consequences of specific intervention is infeasible. We considered four intervention scenarios. The first intervention scenario started intervention on March 24, 2020 with a weight of 0.5, one week later transitioned to a complete intervention with a weight of 1.
The second intervention started with a weight of 0 for the first week, a weight of 0.5 for the second week, and two weeks later transitioned to a complete intervention with a weight of 1.
The third intervention was delaying two weeks, limited in the thrid week and complete in the fourth week. The fourth intervention delayed actions for three weeks, limited in the fourth weeks and complete in the fifth week. For each scenario, we investigated how the degree and timing of the intervention determined the peak time and case ending time, the peak number and maximum number of cases and forecasting the peak and maximum number of new and cumulative cases in more than 150 countries across the world.
The analysis is based on the surveillance data of confirmed cumulative and new Covid-19 cases in the world up to March 16, 2020. Data on the number of cumulative, new and death cases of Covid-19 from January 20, 2020 to March 16 were obtained from WHO (https://www.who.int/emergencies/diseases/novel-coronavirus-2019/situation-reports). Data included the total numbers of cumulated, newly confirmed and attributed deaths across 152 countries.
To demonstrate that the MAE is an accurate forecasting method, the MAE was applied to confirmed accumulated cases of Covid-19 across 152 countries. The intervention indicator for China and other countries was set to 1 and 0, respectively. eTable 1 presented the one-step to five-step errors for forecasting the cumulative cases, starting from March 12, 2020. In all cases, the average forecasting accuracies of the MAE were less than 2.5% (eTable 1). Table 1 
There is urgent need to develop new strategies to curb the spread of COVID-19. 1 We investigate whether complete interventions can control the spread of COVID-19 and how early complete interventions will reduce the peak time and the number, and the final total number of cases across the world. Table 2 
To further illustrate the impact of interventions on the spread of COVID-19, we compared the effects of the four intervention scenarios on the transmission dynamics of Covid-19 across the world. Figure 1 was shifted more than one month to the right and was much steeper than that of under the early intervention. Delaying intervention will substantially increase the number of cumulative cases of Covid-19. eFigure 4 shows the case-fatality rate curve as a function of the Date where the case-fatality rate was defined as the ratio of the number of deaths over the number of cumulative cases in the world. The average case-fatality rate was 3.5%.
Real-time forecasting are more accurate than epidemiologic transmission model where the model parameters may not applicable in practice. We estimated the duration, peak time and ending time, peak number and maximum number of cumulative cases of Covid-19 under four intervention scenarios for 152 countries in the world. This provided critical information for government and health authorities to consider urgent public health response planning to slow the spread of Covid-19. We demonstrated that aggressive interventions are urgently needed.
Otherwise, we will face disastrous consequences.
Covid-19 in the world as a function of days from January 20, 2020 to July 28, 2020. 
Data , where was the observed number of the cases in the forecasting day of the ℎ segment time series and ̂ was its forecasted number of cases by the MAE, and were weights. If was in the interval [1, 12] , then = 1. If was in the interval [13, 24] , then = 2, etc. The back propagation algorithm was used to estimate the weights and bias in the MSAE. Repeat training processed 5 times. The average forecasting ̂, = 1, … , 152 will be taken as a final forecasted number of the accumulated confirmed cases for each country.
The 