Study of the 5th Wave of COVID-19 Outbreak in Thailand Using Mathematical Model

Covid-19 is a contagious disease that is transmitted from person to person through small droplets released when coughing or sneezing. Currently, Thailand is experiencing an outbreak of the Omicron variant of the Covid-19 virus in its fifth wave, with a high number of infected individuals compared to previous waves. Therefore, we are interested to study the spread of the disease and the effectiveness of the three-dose vaccination using Mathematical model. To analyze the spread and study the impact of vaccination, we developed a mathematical model consisting of eight population groups: Susceptible population (S), Vaccinated population at risk (Sv), Infected population with mild symptoms (I), Hospitalized population with severe symptoms (H1), ICU-admitted population in critical condition (C), Hospitalized population recovering from ICU treatment (H2), Recovered population (R), Death population (D). In our investigation of COVID-19 spread and the effectiveness of vaccination, we determined crucial epidemiological factors, including the endemic equilibrium and the basic reproduction number (R0). We then conduct mathematical and numerical analysis of the model. Our findings indicate that the endemic equilibrium is stable whenever R0>1 and unstable when R0<1. Additionally, we performed sensitivity analyses on the model, examining the impact of the basic reproduction number. Notably, parameters τi,mi, and γ demonstrated significant influence on the infection rate (basic reproduction number), while parameters β,η, and sv^i primarily influenced the magnitude of the infected population during an epidemic. Moreover, the first and second vaccine doses have similar effect in controlling the spread of COVID-19, while the complete three-dose vaccination demonstrated superior effectiveness in mitigating transmission compared to vaccination with only one or two doses.