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1.
Viruses ; 14(3)2022 03 04.
Article in English | MEDLINE | ID: covidwho-1732240

ABSTRACT

The omicron variant (B.1.1.529) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was the predominant variant in South Korea from late January 2022. In this study, we aimed to report the early estimates of the serial interval distribution and reproduction number to quantify the transmissibility of the omicron variant in South Korea between 25 November 2021 and 31 December 2021. We analyzed 427 local omicron cases and reconstructed 73 transmission pairs. We used a maximum likelihood estimation to assess serial interval distribution from transmission pair data and reproduction numbers from 74 local cases in the first local outbreak. We estimated that the mean serial interval was 3.78 (standard deviation, 0.76) days, which was significantly shorter in child infectors (3.0 days) compared to adult infectors (5.0 days) (p < 0.01). We estimated the mean reproduction number was 1.72 (95% CrI, 1.60-1.85) for the omicron variant during the first local outbreak. Strict adherence to public health measures, particularly in children, should be in place to reduce the transmission risk of the highly transmissible omicron variant in the community.


Subject(s)
COVID-19 , SARS-CoV-2 , Adult , COVID-19/epidemiology , Child , Humans , Reproduction , Republic of Korea/epidemiology , SARS-CoV-2/genetics
2.
Open Forum Infect Dis ; 8(11): ofab432, 2021 Nov.
Article in English | MEDLINE | ID: covidwho-1584166

ABSTRACT

[This corrects the article DOI: 10.1093/ofid/ofab350.].

3.
Emerg Infect Dis ; 28(2): 407-410, 2022 02.
Article in English | MEDLINE | ID: covidwho-1575455

ABSTRACT

We estimated mean serial interval and superspreading potential for the Delta variant of severe acute respiratory syndrome coronavirus 2 in South Korea. Intervals were similar for the first (3.7 days) and second (3.5 days) study periods. Risk for superspreading events was also similar; 23% and 25% of cases, respectively, seeded 80% of transmissions.


Subject(s)
COVID-19 , SARS-CoV-2 , Humans , Republic of Korea/epidemiology
4.
2021.
Preprint in English | Other preprints | ID: ppcovidwho-295872

ABSTRACT

We estimated mean serial interval and superspreading potential for the predominant Delta variant of SARS-CoV-2. Mean serial intervals were similar with 3.7 and 3.5 days during early and latter periods, respectively. Furthermore, the risk of superspreading events was similar with 23% and 25% of cases seeded 80% of all transmissions.

5.
EuropePMC; 2021.
Preprint in English | EuropePMC | ID: ppcovidwho-294995

ABSTRACT

Background: The delta variant of SARS-CoV-2 is now the predominant variant worldwide. However, its transmission dynamics remain unclear. Methods We analyzed all case patients in local clusters and temporal patterns of viral shedding using contact tracing data from 405 cases associated with the delta variant of SARS-CoV-2 between 22 June and 31 July 2021 in Daejeon, South Korea. Results Overall, half of the cases were aged under 19 years, and 20% were asymptomatic at the time of epidemiological investigation. We estimated the mean serial interval as 3.26 days (95% credible interval 2.92, 3.60), and 12% of the transmission occurred before symptom onset of the infector. We identified six clustered outbreaks, and all were associated with indoor facilities. In 23 household contacts, the secondary attack rate was 63% (52/82). We estimated that 15% (95% confidence interval, 13–18%) of cases seeded 80% of all local transmission. Analysis of the nasopharyngeal swab samples identified virus shedding from asymptomatic patients, and the highest viral load was observed two days after symptom onset. The temporal pattern of viral shedding did not differ between children and adults ( P  = 0.48). Conclusions Our findings suggest that the delta variant is highly transmissible in indoor settings and households. Rapid contact tracing, isolation of the asymptomatic contacts, and strict adherence to public health measures are needed to mitigate the community transmission of the delta variant.

6.
Open Forum Infect Dis ; 8(11): ofab432, 2021 Nov.
Article in English | MEDLINE | ID: covidwho-1550575

ABSTRACT

[This corrects the article DOI: 10.1093/ofid/ofab350.].

7.
J Infect Dis ; 225(5): 793-799, 2022 03 02.
Article in English | MEDLINE | ID: covidwho-1550555

ABSTRACT

BACKGROUND: The Delta variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was the predominant variant worldwide at the time of this study. However, its transmission dynamics were unclear. METHODS: We analyzed 405 local cases infected with the Delta variant of SARS-CoV-2 and temporal patterns of viral shedding identified between 22 June and 31 July 2021 in Daejeon, South Korea. RESULTS: Overall, 20% were presymptomatic at the time of epidemiological investigation. We identified 6 clustered outbreaks, and all were associated with indoor facilities. In 23 household contacts, the secondary attack rate was 63%. We estimated the mean serial interval as 3.26 days (95% credible interval, 2.92-3.60), and 15% (95% confidence interval, 13%-18%) of cases seeded 80% of all local transmission. Analysis of the nasopharyngeal swab samples identified virus shedding from the presymptomatic cases and the highest viral load was observed 2 days after symptom onset. CONCLUSIONS: Our findings suggest that the Delta variant is highly transmissible in indoor settings and households. Rapid contact tracing, isolation of the asymptomatic contacts, strict adherence to public health measures, and increased uptake of coronavirus disease 2019 (COVID-19) vaccination, including booster doses, are needed to reduce community transmission of the Delta variant.


Subject(s)
COVID-19/epidemiology , COVID-19/transmission , Communicable Disease Control/methods , SARS-CoV-2 , Adolescent , Adult , Aged , COVID-19/prevention & control , Child , Child, Preschool , Contact Tracing , Disease Outbreaks , Female , Humans , Incidence , Infant , Infant, Newborn , Male , Middle Aged , Republic of Korea/epidemiology , Reverse Transcriptase Polymerase Chain Reaction , SARS-CoV-2/genetics , Virus Shedding
8.
Open Forum Infect Dis ; 8(7): ofab350, 2021 Jul.
Article in English | MEDLINE | ID: covidwho-1331567

ABSTRACT

To identify the temporal change in the possible risk of superspreading events, we estimated the overdispersion parameter in 2 different periods of the coronavirus disease 2019 pandemic. We determined that the possible risk of superspreading events was reduced 90% during the second epidemic period in South Korea.

9.
J Prev Med Public Health ; 53(6): 405-408, 2020 Nov.
Article in English | MEDLINE | ID: covidwho-967789

ABSTRACT

In epidemiology, the basic reproduction number (R0) is a term that describes the expected number of infections generated by 1 case in a susceptible population. At the beginning of the coronavirus disease 2019 (COVID-19) pandemic, R0 was frequently referenced by the public health community and the wider public. However, this metric is often misused or misinterpreted. Moreover, the complexity of the process of estimating R0 has caused difficulties for a substantial number of researchers. In this article, in order to increase the accessibility of this concept, we address several misconceptions related to the threshold characteristics of R0 and the effective reproduction number (Rt). Moreover, the appropriate interpretation of the metrics is discussed. R0 should be considered as a population-averaged value that pools the contact structure according to a stochastic transmission process. Furthermore, it is necessary to understand the unavoidable time lag for Rt due to the incubation period of the disease.


Subject(s)
Basic Reproduction Number/statistics & numerical data , COVID-19/epidemiology , Communicable Disease Control/statistics & numerical data , Disease Outbreaks/prevention & control , COVID-19/prevention & control , Communicable Diseases, Emerging/prevention & control , Humans , Models, Statistical , Pandemics/prevention & control , Public Health
10.
Int J Environ Res Public Health ; 17(9)2020 04 29.
Article in English | MEDLINE | ID: covidwho-141716

ABSTRACT

Background: In March 2020, overall, 37,000 international students from China, a country at risk of the 2019-novel coronavirus (COVID-19) infection has arrived in Seoul, South Korea. Individuals from the country at risk of COVID-19 infection have been included in the Korean home-quarantine program, but the efficacy of the program is uncertain. Methods: To estimate the possible number of infected individuals within the large influx of international students from China, we used a deterministic compartmental model for epidemic and performed a simulation-based search of different rates of compliance with home-quarantine. Results: Under the home-quarantine program, the number of the infected individuals would reach 40-72 from 12 March-24 March with the arrival of 0.2% of pre-infectious individuals. Furthermore, the number of isolated individuals would peak at 40-64 from 13 March-27 March in Seoul, South Korea. Our findings indicated when incoming international students showed strict compliance with quarantine, epidemics by the international student from China were less likely to occur in Seoul, South Korea. Conclusions: To mitigate possible epidemics, additional efforts to improve the compliance of home-quarantine of the individuals from countries with the virus risk are warranted along with other containment policies.


Subject(s)
Coronavirus Infections/epidemiology , International Educational Exchange , Pneumonia, Viral/epidemiology , Students/statistics & numerical data , COVID-19 , China/ethnology , Humans , Pandemics , Seoul/epidemiology
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