Research Article Studying the Effect of Taking Statins before Infection in the Severity Reduction of COVID-19 with Machine Learning Alireza Davoudi, 1,2 Mohsen Ahmadi , 3 Abbas Sharifi , 4 Roshina Hassantabar, 1,2 Narges Najafi, 1,2 Atefeh Tayebi, 1,2 Hamideh Abbaspour Kasgari, 5 Fatemeh Ahmadi, 1,4 and Marzieh Rabiee 1,2 1 Department of Infectious Diseases, Mazandaran University of Medical Sciences, P.O. Box: 48175-866, Sari, Iran 2 Antimicrobial Resistance Research Center, Communicable Diseases Institute, Mazandaran University of Medical Sciences, Sari, Iran 3 Department of Industrial Engineering, Urmia University of Technology (UUT), P.O. Box: 57166-419, Urmia, Iran 4 Department of Mechanical Engineering, Urmia University of Technology (UUT), P.O. Box: 57166-419, Urmia, Iran 5 Department of Clinical Pharmacy, Mazandaran University of Medical Science, P.O. Box: 48175-866, Sari, Iran Correspondence should be addressed to Abbas Sharifi; abbas.sharifi@mee.uut.ac.ir Received 13 March 2021; Revised 25 April 2021; Accepted 27 May 2021; Published 21 June 2021 Academic Editor: Quan Zou Copyright © 2021 Alireza Davoudi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Statins can help COVID-19 patients’ treatment because of their involvement in angiotensin-converting enzyme-2. The main objective of this study is to evaluate the impact of statins on COVID-19 severity for people who have been taking statins before COVID-19 infection. The examined research patients include people that had taken three types of statins consisting of Atorvastatin, Simvastatin, and Rosuvastatin. The case study includes 561 patients admitted to the Razi Hospital in Ghaemshahr, Iran, during February and March 2020. The illness severity was encoded based on the respiratory rate, oxygen saturation, systolic pressure, and diastolic pressure in five categories: mild, medium, severe, critical, and death. Since 69.23% of participants were in mild severity condition, the results showed the positive effect of Simvastatin on COVID-19 severity for people that take Simvastatin before being infected by the COVID-19 virus. Also, systolic pressure for this case study is 137.31, which is higher than that of the total patients. Another result of this study is that Simvastatin takers have an average of 95.77 mmHg O 2 Sat; however, the O 2 Sat is 92.42, which is medium severity for evaluating the entire case study. In the rest of this paper, we used machine learning approaches to diagnose COVID-19 patients’ severity based on clinical features. Results indicated that the decision tree method could predict patients’ illness severity with 87.9% accuracy. Other methods, including the K -nearest neighbors (KNN) algorithm, support vector machine (SVM), Naïve Bayes classifier, and discriminant analysis, showed accuracy levels of 80%, 68.8%, 61.1%, and 85.1%, respectively. 1. Introduction In late December 2019, a previously unidentified coronavi- rus, currently named the 2019 novel β-coronavirus, emerged from Wuhan, China, the provincial capital of Hubei Prov- ince. The virus was later named severe acute respiratory syn- drome coronavirus 2 (SARS-CoV-2) [1]. The World Health Organization (WHO) first declared the coronavirus disease (named COVID-19) as an international public health emer- gency and then as a pandemic [2]. The disease’s incubation period is from 2 to 14 (average 4 to 7) days [1], and its initial manifestations are related to viremia. The clinical manifesta- tions of COVID-19, which appear after an incubation period of around 5-6 days, are associated with the release of cyto- kines and cytokine storm syndrome in severe cases. The clin- ical spectrum of the disease varies from asymptomatic or mild (in more than 80%) to severe cases, which lead to acute respiratory syndrome, respiratory failure, and death. Clinical features of the disease include fever, coughing, fatigue, sweat- ing, myalgia, sore throat, dry mouth, dry cough, shortness of breath, chest pain, hemoptysis, abdominal pain, nausea, and diarrhea [3]. According to the disease onset, the essential Hindawi BioMed Research International Volume 2021, Article ID 9995073, 12 pages https://doi.org/10.1155/2021/9995073