The Second Wave of COVID-19 in South and Southeast Asia and the Effects of Vaccination

Abstract

Background: By February 2021, the overall impact of coronavirus disease 2019 (COVID-19) in South and Southeast Asia was relatively mild. Surprisingly, in early April 2021, the second wave significantly impacted the population and garnered widespread international attention. Methods: This study focused on the nine countries with the highest cumulative deaths from the disease as of August 17, 2021. We look at COVID-19 transmission dynamics in South and Southeast Asia using the reported death data, which fits a mathematical model with a time-varying transmission rate. Results: We estimated the transmission rate, infection fatality rate (IFR), infection attack rate (IAR), and the effects of vaccination in the nine countries in South and Southeast Asia. Our study suggested that the IAR is still low in most countries, and increased vaccination is required to prevent future waves. Conclusion: Implementing non-pharmacological interventions (NPIs) could have helped South and Southeast Asia keep COVID-19 under control in 2020, as demonstrated in our estimated low-transmission rate. We believe that the emergence of the new Delta variant, social unrest, and migrant workers could have triggered the second wave of COVID-19.

Keywords: COVID-19; Delta variants; South Asia; Southeast Asia; infection attack rate; infection fatality rate; mathematical modeling; vaccination.

Figure 1

Reported confirmed coronavirus disease 2019 (COVID-19) deaths (black curve) in nine countries in SEA and SA, with vaccination coverage. All the vaccinated proportion (red diamond, vaccinated/one plus dose) and fully vaccinated proportion of the population (blue square, fully vaccinated). The first wave of COVID-19 epidemic occurred largely before March 2021, and the second wave of COVID-19 epidemic appeared after March 2021. (A) India, (B) Indonesia, (C) Malaysia, (D) Myanmar, (E) Nepal, (F) Singapore, (G) Sri Lanka, (H) Thailand, (I) Viet Nam.

Figure 2

Percentage of strains sequenced biweekly [strain percentage in seven countries of SA and SEA (A–G)] where variants sequenced data are available (8). We only show these strains with a maximum percentage > 20%. (H) Showed the median of strain percentage for each strain sequenced in the seven countries.

Figure 3

Fitting the model to the reported deaths in India (A), Indonesia (B), Malaysia (C), Myanmar (D), Nepal (E), Singapore (F), Sri Lanka (G), Thailand (H), and Viet Nam (I) with a time-varying transmission rate. The red circles denote the daily reported COVID-19 deaths. The black curve denotes the median of 1,000 model simulations with vaccination, while the green curve shows the simulation median without vaccination. The shaded region denotes the 95% CI of the 1,000 model simulations. The blue-dashed curve denotes the reconstructed transmission rate. ϕ = 0.008 for India; ϕ = 0.03 for other countries. Here, ${\mathcal{R}}_0=\beta (t)/\gamma$. The IFR is shown in each panel and the IAR is shown above each panel.