Universal Journal of Public Health 10(6): 596-605, 2022 DOI: 10.13189/ujph.2022.100607 http://www.hrpub.org A Compartmental Model for Assessing Effects of COVID-19 Vaccination in Thailand Chadaphim Photphanloet 1 , Siriprapa Ritraksa 1 , Sherif Eneye Shuaib 2 , Arthit Intarasit 1 , Pakwan Riyapan 1,* 1 Department of Mathematics and Computer Science, Faculty of Science and Technology, Prince of Songkla University, Pattani, 94000, Thailand 2 Department of Mathematics and Statistics, York University, Toronto, ON M3J 1P3, Canada Received August 2, 2022; Revised November 12, 2022; Accepted November 21, 2022 Cite This Paper in the following Citation Styles (a): [1] Chadaphim Photphanloet, Siriprapa Ritraksa, Sherif Eneye Shuaib, Arthit Intarasit, Pakwan Riyapan, ”A Compartmental Model for Assessing Effects of COVID-19 Vaccination in Thailand,” Universal Journal of Public Health, Vol.10, No.6, pp. 596-605, 2022. DOI: 10.13189/ujph.2022.100607 (b): Chadaphim Photphanloet, Siriprapa Ritraksa, Sherif Eneye Shuaib, Arthit Intarasit, Pakwan Riyapan (2022). A Compartmental Model for Assessing Effects of COVID-19 Vaccination in Thailand. Universal Journal of Public Health, 10(6), 596-605. DOI: 10.13189/ujph.2022.100607 Copyright ©2022 by authors, all rights reserved. Authors agree that this article remains permanently open access under the terms of the Creative Commons Attribution License 4.0 International License Abstract A dynamical model for COVID-19 spread relating to non-pharmaceutical interventions and vaccination is mathematically generated by adding a gradual vaccination compartment for the susceptible population and considering only a symptomatic infectious stage. In our model, there are seven compartments dividing a given population into susceptible (S), vaccinated (V ), exposed (E), infected (I ), quarantined (Q), recovered (R) and death (D) groups, respectively. Then, theoretically analysis is given by investigating the COVID-19 free and endemic equilibrium points, and computing the vacci- nation reproduction number of this model denoted as R vac using the next generation matrix. If R vac > 1, then the COVID-19 transmission increases exponentially and depends on vaccine efficacy. On the other hand, if R vac < 1, then there occurs the COVID-19 disease eradication. The risk from infection can be importantly reduced whenever the intake of COVID-19 vaccines exceeds one dose. The numerical results reveal that the nonpharmaceutical ways and the administered COVID-19 vaccines can be effective against the current variants of COVID-19, and the additional efforts such as a third vaccine booster shot should be considered and implemented to greatly mitigate the risks of emerging variants of the COVID-19 virus. Moreover, combining different types of COVID-19 vaccines can be appeared as a possible way to give better protection against COVID-19 as well. Keywords COVID-19 Vaccination, Disease-free Equilibrium, Endemic Equilibrium, Mathematical Model, Vaccination Re- production Number 1 Introduction Thailand documented its first COVID-19 case on the 13th of January 2020. To reduce the havoc caused by the pandemic on its people, the Thai government assisted its citizens in several ways including a stimulus package with 1.9 trillion-baht (US$60 billion) [1]. After more than a year of ongoing cycles of imposing various travel restrictions (international and provincial) to suppress the pandemic, Thailand is yet to fully recover economically as the pandemic has heavily disrupted the tourism sector that contributes the most to the country’s economy. As of the 31st of December 2021, about 2, 220, 324 confirmed cases and 21, 698 deaths had been documented [2], for a population of 69.8 million inhabitants [3]. On the 7th of June 2021, the Thai government commenced its mass vaccination campaign [4]. As of the 27th of December, at least 73.1% (51,032,649) of the total population has received at least one vaccine dose, 65.1% (45,423,045) were fully vaccinated, and 8.9% (6,226,249) has received a booster shot. COVID-19 vaccinations have declined from the highest government stimulus in late September and early October. Booster shots were quite rare in September when they are mainly given to medical and frontline workers and to those who have to travel abroad. However, with the recent Omicron variant becoming a concern worldwide [5], booster shots have been concentrated by different governments’ vaccination efforts, especially as reporting shows