Comparison of secondary attack rate and viable virus shedding between patients with SARS-CoV-2 Delta and Omicron variants: A prospective cohort study

Sung Woon Kang, Ji Yeun Kim, Heedo Park, So Yun Lim, Jeonghun Kim, Euijin Chang, Seongman Bae, Jiwon Jung, Min Jae Kim, Yong Pil Chong, Sang Oh Lee, Sang Ho Choi, Yang Soo Kim, Man Seong Park, Sung Han Kim

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10 Citations (Scopus)


There are limited data comparing the transmission rates and kinetics of viable virus shedding of the Omicron variant to those of the Delta variant. We compared these rates in hospitalized patients infected with Delta and Omicron variants. We prospectively enrolled adult patients with COVID-19 admitted to a tertiary care hospital in South Korea between September 2021 and May 2022. Secondary attack rates were calculated by epidemiologic investigation, and daily saliva samples were collected to evaluate viral shedding kinetics. Genomic and subgenomic SARS-CoV-2 RNA was measured by PCR, and virus culture was performed from daily saliva samples. A total of 88 patients with COVID-19 who agreed to daily sampling and were interviewed, were included. Of the 88 patients, 48 (59%) were infected with Delta, and 34 (41%) with Omicron; a further 5 patients gave undetectable or inconclusive RNA PCR results and 1 was suspected of being coinfected with both variants. Omicron group had a higher secondary attack rate (31% [38/124] vs. 7% [34/456], p < 0.001). Survival analysis revealed that shorter viable virus shedding period was observed in Omicron variant compared with Delta variant (median 4, IQR [1−7], vs. 8.5 days, IQR [5–12 days], p < 0.001). Multivariable analysis revealed that moderate-to-critical disease severity (HR: 1.96), and immunocompromised status (HR: 2.17) were independent predictors of prolonged viral shedding, whereas completion of initial vaccine series or first booster-vaccinated status (HR: 0.49), and Omicron infection (HR: 0.44) were independently associated with shorter viable virus shedding. Patients with Omicron infections had higher transmission rates but shorter periods of transmissible virus shedding than those with Delta infections.

Original languageEnglish
Article numbere28369
JournalJournal of Medical Virology
Issue number1
Publication statusPublished - 2023 Jan

Bibliographical note

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© 2022 Wiley Periodicals LLC.


  • COVID-19
  • infection dynamics
  • virus shedding

ASJC Scopus subject areas

  • Infectious Diseases
  • Virology


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