//Learning from Japan

Learning from Japan


Dynamic Change of COVID-19 Seroprevalence among Asymptomatic Population in Tokyo during the Second Wave (Tokyo and Boston)


Population 127 million

Cases, 89,650

Deaths, 1,631

Fatality rates, low compared to Western Countries

Decreased despite the absence of lockdown

? low infection prevalence

? low IFR

Seroprevalence among asymptomatic employees, Tokyo

May 26 to August 25

Healthy volunteer workers, n = 1,877

IgM and IgG antibodies, test repeated at a month

Symptomatics excluded




615 healthy volunteers received at least one test

Seroprevalence increased from 5.8 % to 46.8 % over summer

Paralleling the rise in daily confirmed cases within Tokyo

Exclusion of individuals with clinical symptoms, probable underestimation

Peaked on August 4

Peaked with the peak of the second wave

Out of the 350 individuals who completed both offered tests

21.4 % who tested seronegative became seropositive

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

IgM+/IgG- was the least common, 0.4% (3/700 total tests)

Short time frame between developing IgM then developing IgG

None of the seroconverted individuals were hospitalized or died


COVID-19 infection may have spread widely across the general population of Tokyo

Despite the very low fatality rate

Temporal correlation between the rise in seropositivity and the decrease in reported COVID-19 cases

How to explain?

Local observations

Masks culture

Non-tactile culture

Quite culture

Ventilation culture

App use

Limited international travel

Supervised quarantine, 14 days


Why Is the Obesity Rate So Low in Japan and High in the U.S.? (Research Gate)


BMI over 30, international standard for obesity

Japan, 3.6%

US, 32.0%

BMI over 25, overweight

Japan, 24.7%

US, 66.5%

The average person in Japan consumes over 200 fewer calories per day than the average American

Drive less, walk more, use more public transport