Viral load dynamics in asymptomatic and symptomatic patients during Omicron BA.2 outbreak in Shanghai, China, 2022: a longitudinal cohort study

Backgrounds: The SARS-CoV-2 virus has caused global outbreaks, including the recent Omicron BA.2 wave in Shanghai in spring 2022. While, the viral load dynamic of Omicron infections with different clinical severity was still unclear. Methods: A prospective cohort was conducted on 48,830 hospitalized COVID-19 patients in three hospitals in Shanghai, China, from 23 March and 15 May 2022. Regular nucleic acid testing was performed and the Cycle threshold (Ct) value tested by RT-PCR was used as a proxy of viral load. The viral load dynamic by different clinical severity since initial detection and the risk factors were analyzed. Results: The study included 31% asymptomatic cases, 68% mild-moderate cases, 1% severe cases, 1.29% critical and fatal cases. 57% of patients tested positive upon admission, average Ct value remained stable with peak viral concentrations occurring at 4 days (median Ct value of 27.5), followed by a decrease with a viral shedding time (VST) of 6.1 days (IQR, 4.0-8.8 days). Omicron viral load varied by age and clinical severity, but peak Ct values occurred at similar times. Unvaccinated status, age over 60, and comorbidities were associated with higher peak viral concentrations and longer shedding durations. Asymptomatic cases had a 40% contagious probability within 6 days of detection. Mild-moderate cases and severe cases had a 27%, >50% probability of infectiousness post-symptom resolution, respectively. Conclusion: The initial Ct value could forecast severe consequences. Unvaccinated older people with specific comorbidities are the high-risk groups associated with high viral load and long shedding duration. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work was supported by Shanghai Municipal Science and Technology Major Project [HS2021SHZX001], the Key Program of the National Natural Science Foundation of China [82161138018 and 82041010], Shanghai Science and Technology Committee [20dz2260100, 20Z11901100] and Shanghai Hospital Development Center [SHDC2020CR5010-002] and the Key Program of the National Science Foundation of China [82130093]. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: This study was performed in compliance with an institutional review board protocol at Huashan Hospital (KY2022-596). Written informed consent was obtained from each participant. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes The data analyzed are not publicly available as they contain personal information.