J Korean Med Sci.  2022 Oct;37(41):e300. 10.3346/jkms.2022.37.e300.

The Possible Impact of Nationwide Vaccination on Outcomes of the COVID-19 Epidemic in North Korea: A Modelling Study

• Jung Sm
• Jung J

• KMID: 2534462
• DOI: http://doi.org/10.3346/jkms.2022.37.e300

Abstract

Background
The Democratic People’s Republic of Korea (North Korea) had successfully suppressed the coronavirus disease 2019 (COVID-19) epidemic via border closures. However, a rapid surge in incidence was reported due to the spread of the omicron variant (B.1.1.529), leading to a national emergency declaration in May 2022. Moreover, with the lack of vaccine accessibility and medical facilities, it is unclear how the disease burden may be exacerbated. Despite the limited epidemiological data, we aimed to project the COVID-19 transmissions in North Korea and quantify the potential impact of nationwide vaccination, comparing epidemiological outcomes via scenario analysis.
Methods
A discrete-time deterministic compartmental model was used. The parameters were calibrated using empirical data. Numerical simulations incorporated nationwide COVID-19 vaccination into the proposed model with various asymptomatic proportions.
Results
Our model suggested that the stringent public health and social measures (PHSMs) reduced the severe acute respiratory syndrome coronavirus 2 transmissibility by more than 80% in North Korea. Projections that explicitly incorporated vaccination indicated that nationwide vaccination would be necessary to suppress a huge resurgence in both COVID-19 cases and hospitalizations after the stringent PHSMs are eased. Moreover, vaccinating more than 80% of the population with two doses may keep the peak prevalence of hospitalizations below 1,500, averting more than 40,000 hospitalizations across all scenarios.
Conclusion
Nationwide vaccination would be essential to suppress the prevalence of COVID-19 hospitalizations in North Korea after the stringent PHSMs are lifted, especially in the case of a small asymptomatic proportion.

Keyword

COVID-19; Democratic People’s Republic of Korea; Epidemiological Models; Risk Assessment; Vaccination

Figure

• 

  Fig. 1 Probable COVID-19 cases in North Korea by date of reporting. The epidemic curve of probable COVID-19 cases in North Korea by date of reporting is shown. The blue bars represent the empirically observed case counts, and the yellow bars represent the extrapolated case counts based on the exponential growth model. The red lines represent the 95% confidence intervals derived using the parametric bootstrap method.COVID-19 = coronavirus disease 2019.

• 

  Fig. 2 Schematic diagrams for modelling framework. Diagrams showing a compartment model and transition rates for (A) the baseline model and (B) the extended model integrating nationwide vaccination are shown. S, E, I, R, H, and D denote susceptible, exposed, infectious, recovered, hospitalized (severe COVID-19 cases), and deceased states, respectively. Subscript v indicates individuals who are vaccinated with the first dose, and subscript f indicates those who are vaccinated with the second dose. Subscript n indicates the month since the second dose was administered representing the time-varying vaccine effectiveness.COVID-19 = coronavirus disease 2019.

• 

  Fig. 3 Quantified impact of stringent PHSMs on SARS-CoV-2 transmission in North Korea. The quantified impact of stringent PHSMs enacted on 14 May 2022 on the SARS-CoV-2 transmissions in North Korea are shown with varied proportions of asymptomatic cases (range 30–50%). (A, B) The number of newly reported probable cases, and (C, D) the prevalence of severe cases are shown. The grey bars show the empirically observed number of newly reported cases (A, B). The colored lines and shaded areas show the projected transmission dynamics of COVID-19 based on different effects of the stringent PHSMs (i.e., the reduction levle in the transmissibility of SARS-CoV-2) and 95% confidence intervals derived using the parametric bootstrap method despite small uncertainties surrounding parameters.PHSM = public health and social measure, SARS-CoV-2 = severe acute respiratory syndrome coronavirus 2.

• 

  Fig. 4 Projected impact of nationwide vaccination on SARS-CoV-2 transmission in North Korea. The projected impact of nationwide vaccination on SARS-CoV-2 transmission in North Korea are shown, assuming the stringent PHSMs reduce the transmissibility of SARS-CoV-2 by 80% (k = 0.2), and that the stringent PHSMs will be lifted after a fraction of the population receive at least a single dose of the vaccine. Two epidemiological outcomes are shown by varying both the proportions of asymptomatic cases (range, 30–50%) and the vaccination coverage (range, 0–80%). (A, B) The number of newly reported probable cases and (C, D) the prevalence of severe cases are shown. In scenarios without nationwide vaccination, the stringent PHSMs are modelled to be lifted on the same date as scenarios with 50% of vaccination coverage, and the PHSMs placed prior to 14 May 2020 are expected to be maintained (k = 1). The grey bars show the empirically observed number of newly reported cases (A, B). The colored lines and shaded areas show the projected transmission dynamics of COVID-19 based on different vaccination coverage with two doses and 95% confidence intervals derived using the parametric bootstrap method despite small uncertainties surrounding parameters. The dashed lines show the date when the stringent PHSMs are lifted in each projection.SARS-CoV-2 = severe acute respiratory syndrome coronavirus 2, PHSM = public health and social measure, COVID-19 = coronavirus disease 2019.

• 

  Fig. 5 Averted epidemiological outcomes of COVID-19 following nationwide vaccination in North Korea.The averted epidemiological outcomes of COVID-19 as a result of the introduction of nationwide vaccination from 1 June to 31 October 2022 are shown. Three epidemiological outcomes achieved by varying both the proportions of asymptomatic cases (range, 30–50%) and the vaccination coverage (range, 0–80%) are shown. (A) The number of probable cases, (B) hospitalizations, and (C) COVID-19-related deaths are shown. The cumulative epidemiological outcomes of each projection are compared with those of the projected outcomes without nationwide vaccination based on the median value of each estimated parameter (i0, r, and β).COVID-19 = coronavirus disease 2019.

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