Reconstruction of the transmission dynamics of the first COVID-19 epidemic wave in Thailand

Abstract

Thailand was the first country reporting the first Coronavirus disease 2019 (COVID-19) infected individual outside mainland China. Here we delineated the course of the COVID-19 outbreak together with the timeline of the control measures and public health policies employed by the Thai government during the first wave of the COVID-19 outbreak in Thailand. Based on the comprehensive epidemiological data, we reconstructed the dynamics of COVID-19 transmission in Thailand using a stochastic modeling approach. Our stochastic model incorporated the effects of individual heterogeneity in infectiousness on disease transmission, which allows us to capture relevant features of superspreading events. We found that our model could accurately capture the transmission dynamics of the first COVID-19 epidemic wave in Thailand. The model predicted that at the end of the first wave, the number of cumulative confirmed cases was 3091 (95%CI: 2782–3400). We also estimated the time-varying reproduction number (Rt) during the first epidemic wave. We found that after implementing the nationwide interventions, the Rt in Thailand decreased from the peak value of 5.67 to a value below one in less than one month, indicating that the control measures employed by the Thai government during the first COVID-19 epidemic wave were effective. Finally, the effects of transmission heterogeneity and control measures on the likelihood of outbreak extinction were also investigated.

Estimation of Excess All-Cause Mortality Due to COVID-19 in Thailand

“…The disease then spread swiftly across the globe in early 2020. Thailand was the first country to report a COVID-19-infected person outside of mainland China and has recently experienced the most prominent COVID-19 outbreak in 2021 [ 3 , 4 , 5 ]. To mitigate the disease transmission, the Thai government implemented social distancing and stringent lockdown measures throughout the country and imposed international travel restrictions and nighttime curfews [ 6 ].…”

Heterologous vaccination as a strategy to minimize inequity in COVID-19 vaccine access: A modeling study in Thailand

“…Since the first infected case of COVID-19 was detected in Thailand in early 2020, two waves of the epidemic were well managed and controlled, with 29,127 cumulative cases and 95 deaths as of March 29, 2021. Early April 2021, the third wave of transmission began with the imported Delta variant [12, 36]. The Delta variant led to rising confirmed reported cases from February 28 to November 31, 2021 ( Figure 2a ).…”

“…However, if the vaccine rollout speed is slow (in the range of 50,000-100,000 doses/day), vaccinating the elderly first can drastically reduce mortality more than other strategies ( Figure 6 ). Indeed, Thailand has implemented a very strict lockdown combined with case isolation and non-pharmaceutical interventions such as physical distancing and face masking during the COVID-19 outbreak [12, 36, 50]. This has resulted in a low effective reproduction number during the outbreak ( Figure 2d ).…”

“…We estimated the time-varying reproduction number (Rt), which is the average number of secondary cases generated by an infected person. A value of Rt greater than the threshold value of 1 indicates that the number of new infections is growing at time t, whereas Rt less than 1 indicates that the epidemic size is shrinking at time t. We employed a method proposed by Cori and colleagues [36,38] to estimate the Rt in Thailand. Rt was calculated starting from April 5, when the number of daily cases exceeded 100, to December 1, 2021 (Figure 2d).…”

“…Indeed, Thailand has implemented a very strict lockdown combined with case isolation and nonpharmaceutical interventions such as physical distancing and face masking during the COVID-19 outbreak [12,36,50]. This has resulted in a low effective reproduction number during the outbreak (Figure 2d).…”