Evaluating the Impact of Intervention Strategies on the First Wave and Predicting the Second Wave of COVID-19 in Thailand: A Mathematical Modeling Study

SIMPLE SUMMARY: The world is currently experiencing the COVID-19 pandemic, consequently, we developed a compartmental model to describe the transmission dynamic of the disease, which can reproduce the incidence of COVID-19 first wave in Thailand. Screening incoming visitors, contact tracing, and case investigation were introduced from the beginning of the pandemic, while the rapid reduction of new cases was a result of the declaration of emergency decree in March 2020. The validated model was used to quantify the impacts of these intervention strategies. The model predicted that the daily reported incidence would have reached zero by the end of June if the on-going non-pharmaceutical interventions (NPIs) were strictly and widely implemented. Our study provides a better understanding of the first wave COVID-19 pandemic and the impacts of government interventions in a Thai setting, where data were still limited. The model further explored the use of these available interventions in the scenario analysis to control the emergence of a second wave of COVID-19 in Thailand. Continued good practice of social distancing to minimize the contact rates is still necessary while the vaccines are not fully available to all populations. ABSTRACT: Coronavirus disease 2019 (COVID-19) has spread rapidly worldwide. This study aimed to assess and predict the incidence of COVID-19 in Thailand, including the preparation and evaluation of intervention strategies. An SEIR (susceptible, exposed, infected, recovered) model was implemented with model parameters estimated using the Bayesian approach. The model’s projections showed that the highest daily reported incidence of COVID-19 would be approximately 140 cases (95% credible interval, CrI: 83–170 cases) by the end of March 2020. After Thailand declared an emergency decree, the numbers of new cases and case fatalities decreased, with no new imported cases. According to the model’s predictions, the incidence would be zero at the end of June if non-pharmaceutical interventions (NPIs) were strictly and widely implemented. These stringent NPIs reduced the effective reproductive number (Rt) to 0.73 per day (95% CrI: 0.53–0.93) during April and May. Sensitivity analysis showed that contact rate, hand washing, and face mask wearing effectiveness were the parameters that most influenced the number of reported daily new cases. Our evaluation shows that Thailand’s intervention strategies have been highly effective in mitigating disease propagation. Continuing with these strict disease prevention behaviors could minimize the risk of a new COVID-19 outbreak in Thailand.