Research Article Estimating the Number of COVID-19 Cases and Impact of New COVID-19 Variants and Vaccination on the Population in Kerman, Iran: A Mathematical Modeling Study Mehran Nakhaeizadeh , 1,2 Maryam Chegeni , 3,4 Masoumeh Adhami, 1 Hamid Sharifi , 5 Milad Ahmadi Gohari , 1,2 Abedin Iranpour , 5 Mahdieh Azizian , 1,6 Mashaallah Mashinchi , 7 Mohammad Reza Baneshi , 1,8 Mohammad Karamouzian , 5,9 Ali Akbar Haghdoost , 10 and Yunes Jahani 1,2 1 Modeling in Health Research Center, Institute for Futures Studies in Health, Kerman University of Medical Sciences, Kerman, Iran 2 Department of Biostatistics and Epidemiology, School of Public Health, Kerman University of Medical Sciences, Kerman, Iran 3 Department of Basic and Medical Laboratory Sciences, Khomein University of Medical Sciences, Khomein, Iran 4 Molecular and Medicine Research Center, Khomein University of Medical Sciences, Khomein, Iran 5 HIV/STI Surveillance Research Center, and WHO Collaborating Center for HIV Surveillance, Institute for Futures Studies in Health, Kerman University of Medical Sciences, Kerman, Iran 6 Department of General Educations, Afzalipour School of Medicine, Kerman University of Medical Sciences, Kerman, Iran 7 Department of Statistics, Faculty of Mathematics and Computer, Shahid Bahonar University of Kerman, Kerman, Iran 8 School of Public Health, The University of Queensland, Brisbane, Queensland, Australia 9 Brown School of Public Health, Brown University, Providence, RI, USA 10 Social Determinants of Health Research Center, Institute for Futures Studies in Health, Kerman University of Medical Sciences, Kerman, Iran Correspondence should be addressed to Yunes Jahani; u.jahani@kmu.ac.ir Received 1 January 2021; Revised 24 November 2021; Accepted 9 February 2022; Published 26 April 2022 Academic Editor: Marko Gosak Copyright © 2022 Mehran Nakhaeizadeh 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. COVID-19 is spreading all over Iran, and Kerman is one of the most affected cities. We conducted this study to predict COVID- 19-related deaths, hospitalization, and infected cases under different scenarios (scenarios A, B, and C) by 31 December 2021 in Kerman. We also aimed to assess the impact of new COVID-19 variants and vaccination on the total number of COVID-19 cases, deaths, and hospitalizations (scenarios D, E, and F) using the modified susceptible-exposed-infected-removed (SEIR) model. We calibrated the model using deaths reported from the start of the epidemic to August 30, 2021. A Monte Carlo Markov Chain (MCMC) uncertainty analysis was used to estimate 95% uncertainty intervals (UI). We also calculated the time- varying reproductive number (R t ) following time-dependent methods. Under the worst-case scenario (scenario A; contact rate = 10, self ‐isolation rate = 30%, and average vaccination shots per day = 5,000), the total number of infections by December 31, 2021, would be 1,625,000 (95% UI: 1,112,000–1,898,000) with 6,700 deaths (95% UI: 5,200–8,700). With the presence of alpha and delta variants without vaccine (scenario D), the total number of infected cases and the death toll were estimated to be 957,000 (95% UI: 208,000–1,463,000) and 4,500 (95% UI: 1,500–7,000), respectively. If 70% of the population were vaccinated when the alpha variant was dominant (scenario E), the total number of infected cases and deaths would be 608,000 (95% UI: 122,000–743,000) and 2,700 (95% UI: 700–4,000), respectively. The R t was ≥1 almost every day during the epidemic. Our results suggest that policymakers should concentrate on improving vaccination and interventions, such as reducing social contacts, stricter limitations for gathering, public education to promote social distancing, incensing case finding and contact tracing, effective isolation, and quarantine to prevent more COVID-19 cases, hospitalizations, and deaths in Kerman. Hindawi Computational and Mathematical Methods in Medicine Volume 2022, Article ID 6624471, 11 pages https://doi.org/10.1155/2022/6624471