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.
COVID-19 infection may have spread widely across the general population of Tokyo despite the very low fatality rate.
In other words, nearly half of this (masked) population came up positive for antibodies to COVID-19. That’s after excluding anyone with symptoms.
If masks are effective when used by the general public, how did the world’s most competent and experienced users of masks end up transmitting this virus to each other at these rates?