Figures on the number of people testing positive for COVID-19 are published daily in Japan. But because testing is voluntary, the numbers are likely to exclude people who are infected but are asymptomatic.

To get a better idea of the prevalence of asymptomatic infection, a team of researchers at the Tokyo Foundation for Policy Research and elsewhere conducted sentinel surveillance (randomly testing a cross section of the population) of 1 million individuals in Japan and published their results in JAMA Network Open, published by the American Medical Association.

Authored by Research Director Kenji Shibuya, CEO Yuichirio Anzai, and other renowned researchers, the paper notes that while prevalence of asymptomatic infection in Japan was generally lower than in other countries, the findings point to a need to expand PCR and other tests—especially among high-risk groups—to ascertain the true state of infection in the community and to prepare for future surges.

“Prevalence of Asymptomatic SARS-CoV-2 Infection in Japan,” JAMA Network Open
https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2799948

Profile of Research Director Kenji Shibuya
https://www.tokyofoundation.org/experts/detail.php?id=653

Profile of Executive Director and CEO Yuichiro Anzai
https://www.tokyofoundation.org/files/news/Yuichiro%20Anzai%20Profile.pdf