key: cord-0025371-vspnvumr
authors: Lee, Ji Joo; Choe, Young June; Jeong, Hyeongseop; Kim, Moonsu; Kim, Seonggon; Yoo, Hanna; Park, Kunhee; Kim, Chanhee; Choi, Sojin; Sim, JiWoo; Park, Yoojin; Huh, In Sil; Hong, Gasil; Kim, Mi Young; Song, Jin Su; Lee, Jihee; Kim, Eun-Jin; Rhee, Jee Eun; Kim, Il-Hwan; Gwack, Jin; Kim, Jungyeon; Jeon, Jin-Hwan; Lee, Wook-Gyo; Jeong, Suyeon; Kim, Jusim; Bae, Byungsik; Kim, Ja Eun; Kim, Hyeonsoo; Lee, Hye Young; Lee, Sang-Eun; Kim, Jong Mu; Park, Hanul; Yu, Mi; Choi, Jihyun; Kim, Jia; Lee, Hyeryeon; Jang, Eun-Jung; Lim, Dosang; Lee, Sangwon; Park, Young-Joon
title: Importation and Transmission of SARS-CoV-2 B.1.1.529 (Omicron) Variant of Concern in Korea, November 2021
date: 2021-12-21
journal: J Korean Med Sci
DOI: 10.3346/jkms.2021.36.e346
sha: 40d85b5e36a121b8bd0e8d99e78101878f6c7449
doc_id: 25371
cord_uid: vspnvumr

In November 2021, 14 international travel-related severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) B.1.1.529 (omicron) variant of concern (VOC) patients were detected in South Korea. Epidemiologic investigation revealed community transmission of the omicron VOC. A total of 80 SARS-CoV-2 omicron VOC-positive patients were identified until December 10, 2021 and 66 of them reported no relation to the international travel. There may be more transmissions with this VOC in Korea than reported.

exposure, and the serial interval was estimated based on the time from symptom onset in index cases to symptom onset in corresponding contacts.

During November 24 -December 10, 2021, a total of 80 SARS-CoV-2 omicron VOC-positive patients were identified in Korea ( Table 1 ). In total, 14 (17.5%) patients had history of international travels within 14 days of symptom onset, or if asymptomatic, SARS-CoV-2 test results (Nigeria, n = 10; South Africa, n = 2; Mozambique, n = 1; Ethiopia, n = 1, Iran, n = 1; Fig. 1A ). Among community transmission cases, 26 were from households, and 12 were from church-related clusters (Fig. 1B) . Among 78 patients with documented history of vaccination, 48 (60.0%) were unvaccinated, and 25 (31.3%) were vaccinated. The vaccinated persons have received BNT162b (n = 13), mRNA-1273 (n = 5), Ad26.COV2.S (n = 4), and ChAdOx1 (n = 3) vaccines ( Table 1) .

Most of the first 80 SARS-CoV-2 omicron VOC-positive patients were with mild symptoms, and 27.5% were asymptomatic, and no cases were with severe diseases nor death during 6.1 mean observed days (range, 2-16 days). Estimated incubation period was 4.2 days (range, 2-8 days) and serial interval was 2.8 days (range, 1-7 days). 

The authors have no potential conflicts of interest to disclose. Epidemiologic features of the omicron VOC have not been fully characterized in other places. 3 Our finding of short serial interval of 2.8 days is in line with findings from South Africa, with growing reproductive number compared to the delta VOC. 4 Meanwhile, none of the first 80 patients underwent severe disease or death as in the US, which was reassuring, yet, should be monitored further. 5 The hypothesis of trade-off between virulence and transmissibility has been proposed decades ago, which may be supportive to the evolution of SARS-CoV-2 in the long term. 6

Note that 60% of omicron VOC-positive patients were unvaccinated, which emphasizes the need for vaccination to limit the transmission. Yet, given the high rates of mutation that omicron VOC carries, vaccine effectiveness should be investigated further. 7 Earlier findings from South Africa suggest the efficacy of coronavirus disease 2019 vaccine may be significantly reduced against omicron VOC. 

World Health Organization. Tracking SARS-CoV-2 variants

Contact tracing during coronavirus disease outbreak, South Korea

Probable transmission of SARS-CoV-2 Omicron variant in Quarantine Hotel

How bad is Omicron? What scientists know so far

SARS-CoV-2 B.1.1.529 (Omicron) Variant -United States

Beyond Omicron: what's next for COVID's viral evolution

Omicron (B.1.1.529): infectivity, vaccine breakthrough, and antibody resistance

Covid-19: do vaccines work against omicron-and other questions answered

Because information about these early cases of SARS-CoV-2 omicron VOC are selected from import-related incidents, our interpretation should be made cautiously. Moreover, given the relatively short observation time, further follow-up is needed to ascertain the disease severity of this specific VOC as more data are reported globally.In summary, importation of SARS-COV-2 omicron VOC has caused a substantial community transmission in Korea, especially among unvaccinated persons. Although the initial findings on clinical features are reassuring, continuous monitoring of the disease epidemiology and vaccine effectiveness should be in place.

The present study used the quarantine data which were constructed as a legally mandated public health investigation under the authority of the Korean Infectious Diseases Control and Prevention Act (No. 12444 and No. 13392). The study protocol was reviewed and approved by Institutional Review Board of the Korea Disease Control and Prevention Agency (2021-12-05-PE-A).