Dynamic Change of COVID-19 Seroprevalence among Asymptomatic Population in Tokyo during the Second Wave
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Abstract
Importance
Fatality rates related to COVID-19 in Japan have been low compared to Western Countries and have decreased despite the absence of lockdown. Serological tests monitored across the course of the second wave can provide insights into the population-level prevalence and dynamic patterns of COVID-19 infection.
Objective
To assess changes in COVID-19 seroprevalence among asymptomatic employees working in Tokyo during the second wave.
Design
We conducted an observational cohort study. Healthy volunteers working for a Japanese company in Tokyo were enrolled from disparate locations to determine seropositivity against COVID19 from May 26 to August 25, 2020. COVID-19 IgM and IgG antibodies were determined by a rapid COVID19 IgM/IgG test kit using fingertip blood. Across the company, tests were performed and acquired weekly. For each participant, serology tests were offered twice, separated by approximately a month, to provide self-reference of test results and to assess for seroconversion and seroreversion.
Setting
Workplace setting within a large company.
Participants
Healthy volunteers from 1877 employees of a large Japanese company were recruited to the study from 11 disparate locations across Tokyo. Participants having fever, cough, or shortness of breath at the time of testing were excluded.
Main Outcome(s) and Measure(s)
Seropositivity rate (SPR) was calculated by pooled data from each two-weeks window across the cohort. Either IgM or IgG positivity was defined as seropositive. Changes in immunological status against SARS-CoV-2 were determined by comparing results between two tests obtained from the same individual.
Results
Six hundred fifteen healthy volunteers (mean + SD 40.8 + 10.0; range 19 - 69; 45.7 % female) received at least one test. Seroprevalence increased from 5.8 % to 46.8 % over the course of the summer. The most dramatic increase in SPR occurred in late June and early July, paralleling the rise in daily confirmed cases within Tokyo, which peaked on August 4. Out of the 350 individuals (mean + SD 42.5 + 10.0; range 19 - 69; 46.0 % female) who completed both offered tests, 21.4 % of those individuals who tested seronegative became seropositive and seroreversion was found in 12.2 % of initially seropositive participants. 81.1% of IgM positive cases at first testing became IgM negative in approximately one month.
Conclusions and Relevance
COVID-19 infection may have spread widely across the general population of Tokyo despite the very low fatality rate. Given the temporal correlation between the rise in seropositivity and the decrease in reported COVID-19 cases that occurred without a shut-down, herd immunity may be implicated. Sequential testing for serological response against COVID-19 is useful for understanding the dynamics of COVID-19 infection at the population-level.
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SciScore for 10.1101/2020.09.21.20198796: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement IACUC: An outside ethical committee reviewed and approved the protocol. Randomization not detected. Blinding not detected. Power Analysis not detected. Sex as a biological variable Six hundred fifteen healthy volunteers (mean ± SD 40.8 ± 10.0, range 19 - 69; 45.7 % female) out of 1877 employees of a large Japanese company from 11 disparate locations across Tokyo were enrolled. Table 2: Resources
No key resources detected.
Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).
Results from LimitationRecognizer: We detected the following sentences addressing …SciScore for 10.1101/2020.09.21.20198796: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement IACUC: An outside ethical committee reviewed and approved the protocol. Randomization not detected. Blinding not detected. Power Analysis not detected. Sex as a biological variable Six hundred fifteen healthy volunteers (mean ± SD 40.8 ± 10.0, range 19 - 69; 45.7 % female) out of 1877 employees of a large Japanese company from 11 disparate locations across Tokyo were enrolled. Table 2: Resources
No key resources detected.
Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).
Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:This study has some limitations. First, the cohort was a sampling of a single large company in Tokyo and not of the population, in general. Second, detailed medical histories and behavioral patterns of each employee were not obtained. Such information would have helped understand the role of cross-exposure and the factors associated with reduced fatality. Third, our antibody test is qualitative and not quantitative. Therefore, negative results indicate neither the complete loss of antibody nor of immune memory. Further studies using a quantitative antibody measurement are required. Although the COVID-19 vaccine provides a more robust and persistent antibody response8,9, extensive coverage of the general population by vaccination is critical to eradicating COVID-19 from the community, especially if the antibody response is generally short-lived.
Results from TrialIdentifier: No clinical trial numbers were referenced.
Results from Barzooka: We did not find any issues relating to the usage of bar graphs.
Results from JetFighter: We did not find any issues relating to colormaps.
Results from rtransparent:- Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
- Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
- No protocol registration statement was detected.
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