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Viral Kinetics of Symptomatic COVID-19 Cases Infected with the Ancestral Strain and Omicron BA.2
30 Pages Posted: 28 Nov 2022More...
Background: Assessment of viral kinetics of SARS-CoV-2 may inform host immune responses to and transmission potential of the virus. Temporal profiles of viral shedding remain unclear in relation to patient characteristics, type of virus and vaccination status including vaccine type.
Methods: We analyzed longitudinal data on cycle threshold (Ct) values of reverse transcription quantitative polymerase chain reaction (RT-qPCR) assays conducted for symptomatic COVID-19 patients at confirmation and during hospital isolation in Hong Kong during three major epidemic waves predominated by the ancestral strain or Omicron BA.2, and modeled the temporal trajectories of viral burden in these patients.
Findings: Among 19,205 symptomatic COVID-19 cases confirmed from July 1, 2020 to May 22, 2022, the estimated viral burden from a random-effects model indicated a longer duration of viral shedding in more severe and older cases. Vaccinated individuals with a breakthrough infection of Omicron BA.2 had a generally lower viral burden following onset and shorter durations of viral shedding (mean difference of 2-4 days) than the unvaccinated Omicron cases particularly in more recently vaccinated patients. Marginal differences in viral burden following onset and the duration of viral shedding were observed between unvaccinated cases infected with the ancestral strain and Omicron BA.2.
Interpretation: The viral kinetics characterized in our study demonstrated that previously vaccinated younger individuals with a milder infection shed less viruses in a shorter period implying possible transmission dynamics of COVID-19 and protective mechanisms of vaccination against infection and severe outcomes.
Funding Information: This study was supported by the Health and Medical Research Fund from the Health Bureau of the Government of the Hong Kong Special Administrative Region (grant no. CID-HKU2) and the Collaborative Research Fund from the Research Grants Council of the Hong Kong Special Administrative Region (grant no. C7123- 20G).
Declaration of Interests: BJC consults for AstraZeneca, Fosun Pharma, GlaxoSmithKline, Moderna, Pfizer, Roche, and Sanofi Pasteur. The authors declare no other competing interests.
Ethics Approval Statement: Our project was approved by the Institutional Review Board of the University of Hong Kong and Hospital Authority Hong Kong West Cluster.
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