Limitations:
First, this study predicted the total number of cases in the USA, where each country has its’ own number of cases. Prediction for individual countries needs different ARIMA models for each country. Second, Covid-19 is dynamic, using data from different time periods for model building and validation may lead to models with different AR, MA, and differencing components with different validations. Third, we don’t know if we used the variables from the whole or just the tip of the iceberg of cases, but we know that we used all confirmed cases which is more scientifically sound.