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Transmission and Infectious SARS-CoV-2 Shedding Kinetics in Vaccinated and Unvaccinated Individuals

Educational Objective
To identify the key insights or developments described in this article
1 Credit CME
Key Points

Question  Do individuals fully vaccinated against COVID-19 have a shorter duration of viable SARS-CoV-2 viral shedding and a lower rate of secondary transmission than in partially vaccinated or unvaccinated individuals?

Findings  In this cohort study of 173 health care workers, inpatients, and guardians and 45 participants in a community facility, secondary transmission of SARS-CoV-2 was significantly less common, and viable virus was detected for a shorter duration in fully vaccinated individuals than in partially vaccinated or unvaccinated individuals.

Meaning  Fully vaccinated individuals had a shorter duration of viable viral shedding and a lower rate of secondary transmission than partially vaccinated or unvaccinated individuals.

Abstract

Importance  Data are limited on whether patients with breakthrough COVID-19 infection have the potential to significantly contribute to the spread of SARS-CoV-2.

Objective  To compare the secondary attack rate and infectious viral shedding kinetics of SARS-CoV-2 between fully vaccinated individuals (breakthrough infection group) and partially or unvaccinated individuals (nonbreakthrough infection group).

Design, Setting, and Participants  This cohort study assessed secondary transmission by analyzing the epidemiologic data of health care workers, inpatients, and caregivers diagnosed with COVID-19 during hospitalization or residence in a tertiary care hospital between March 1, 2020, and November 6, 2021. To evaluate viral shedding kinetics, the genomic RNA of SARS-CoV-2 was measured using polymerase chain reaction and performed virus culture from daily saliva samples of individuals with mild COVID-19 infected with the Delta variant who were isolated in a community facility in Seoul, South Korea, between July 20 and August 20, 2021.

Exposures  COVID-19 vaccination.

Main Outcomes and Measures  The secondary attack rate and infectious viral shedding kinetics according to COVID-19 vaccination status.

Results  A total of 173 individuals (median [IQR] age, 47 [32-59] years; 100 female [58%]) with COVID-19 were included in the secondary transmission study, of whom 50 (29%) had a breakthrough infection. Secondary transmission was significantly less common in the breakthrough infection group than in the nonbreakthrough infection group (3 of 43 [7%] vs 29 of 110 [26%]; P = .008). In the viral shedding kinetics study, 45 patients (median age, 37 years [IQR, 25-49 years]; 14 female [31%]) infected with the Delta variant were included, of whom 6 (13%) were fully vaccinated and 39 (87%) were partially or unvaccinated. Although the initial genomic viral load was comparable between the 2 groups, viable virus in cell culture was detected for a notably longer duration in partially vaccinated (8 days after symptom onset) or unvaccinated (10 days after symptom onset) individuals compared with fully vaccinated individuals (4 days after symptom onset).

Conclusions and Relevance  In this cohort study, although the initial genomic viral load was similar between vaccinated and unvaccinated individuals, fully vaccinated individuals had a shorter duration of viable viral shedding and a lower secondary attack rate than partially vaccinated or unvaccinated individuals. Data from this study provide important evidence that despite the possibility of breakthrough infections, COVID-19 vaccinations remain critically useful for controlling the spread of SARS-CoV-2.

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Article Information

Accepted for Publication: March 31, 2022.

Published: May 24, 2022. doi:10.1001/jamanetworkopen.2022.13606

Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2022 Jung J et al. JAMA Network Open.

Corresponding Authors: Sung-Han Kim, MD, Department of Infectious Diseases, Asan Medical Center, University of Ulsan College of Medicine, 88 Olympic-ro, 43-gil, Songpa-gu, Seoul 05505, South Korea (kimsunghanmd@hotmail.com); Man-Seong Park, PhD, Department of Microbiology and Institute for Viral Diseases, Korea University College of Medicine, 73 Goryeodae-ro, Seongbuk-gu, Seoul 02841, Republic of Korea (manseong.park@gmail.com).

Author Contributions: Drs Jung and S.-H. Kim had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Drs Jung, J.-Y. Kim, H. Park, and S. Park contributed equally to the work.

Concept and design: Jung, E. Kim, M. Park, S. Kim.

Acquisition, analysis, or interpretation of data: All authors.

Drafting of the manuscript: Jung, H. Park, S. Park, E. Kim, Jieuni Kim, M. Park, S. Kim.

Critical revision of the manuscript for important intellectual content: Ji Yeun Kim, J. Lim, S. Lim, Bae, Y. Lim, M. Park, S. Kim.

Statistical analysis: Jung, H. Park, S. Park, S. Lim, Bae, E. Kim.

Obtained funding: M. Park, S. Kim.

Administrative, technical, or material support: Ji Yeun Kim, H. Park, Jieuni Kim, M. Park.

Supervision: Ji Yeun Kim, Y. Lim, M. Park.

Conflict of Interest Disclosures: None reported.

Funding/Support: This study was supported by grants 2020M3H8A1115041 from the Korea Advanced Research Program through the National Research Foundation of Korea, which is funded by the Ministry of Science and Information and Communication Technologies, Republic of Korea, and by grant and NRF-2017M3A9E4061995 from the National Research Foundation of Korea, which is funded by the Ministry of Science and Information and Communication Technologies, Republic of Korea.

Role of the Funder/Sponsor: The funding sources had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

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