How did Japan sidestep COVID-19's worst
without a hard lockdown?
Last Updated 5 June, 2020. Cellspect Co., Ltd.
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“With this unique Japanese approach, we were able to control this infection trend in just 1.5 months; I think this has shown the power of the Japanese model,” Prime Minister Shinzo Abe declared at a press conference in the evening of May 25 announcing the lifting of the state of emergency.
Japan was once expected to be the most likely outbreak area of COVID-19 because it is geographically close to China, received 925,000 Chinese visitors in January plus a further 89,000 in February, is very densely populated with the world’s oldest population and no hard lockdown policy carried on.) Although Japan’s response against the COVID-19 pandemic has been widely criticized, by luck or by design, this nation has been truly spared the devastating novel coronavirus outbreak taking place in other parts of the world.
There are still many uncertain guesses about the reason, but we can find many very constructive points from the paper published by Professor Iwasaki of Yale University. In this study, she concluded the following hypotheses and evidences: 
1. Japanese culture is inherently suited for social distancing, and face mask use prevents viral spread.
Japanese customs do not involve handshaking, hugging, or kissing when greeting. In addition, many Japanese wear masks through winter to spring to prevent influenza or pollen allergy. A hint to whether this is a valid hypothesis comes from looking at other pandemic viral respiratory diseases. An observational study of elementary school children in Japan found that wearing masks had significant protective association against seasonal influenza. A new study published in the Lancet also support this theory that wearing face masks and social distancing actually reduce COVID-19 spread by 85%.  WHO is also considering changing guidance on wearing face masks.
2. Japanese people were exposed to a milder version of SARS‐CoV‐2 that conferred herd immunity before the spread of a more virulent strain of CoV2.
There is no clear evidence that milder strains of SARS‐CoV‐2 exist but a recent study from the Los Alamos National Laboratory suggested that one particular mutation of SARS-CoV-2, D614G, may make the disease more infectious. D614G began spreading in Europe in early February, and when introduced to new regions it rapidly becomes the dominant form.  This corresponds to Prof. Iwasaki’s finding that there is a large gap in Japan as well as other Asian countries like Thailand, Singapore etc. in between early cases (January–February) and cases in March which are linked to introductions from Europe. 
3. BCG vaccine used in Japan confers protection against COVID‐19.
Prof. Iwasaki indicated that Japan, like many other countries including China, Korea, India have mandatory childhood BCG vaccines against tuberculosis. These countries have so far a relatively low mortality rate from COVID‐19.  The prevalence and mortality rate of COVID-19 was highest in countries that never administered the BCG vaccine such as the United States and Italy, followed by countries that used to vaccinate in the past, including Germany and Australia. What further distinguishes Japan is that the BCG vaccine strain used in Japan, Brazil, and Russia is one of the original strains, while further modified BCG strains are used for vaccination in European countries. This hypothesis is supported by a recent study of Tsuyoshi Miyakawa at Fujita Health University.  The research found that the number of coronavirus cases and deaths per million people was significantly associated with national BCG vaccination policies. "The BCG vaccine is believed to strengthen part of the immune system," Miyakawa said. "Our study supports the theory that the vaccine may be effective against the novel coronavirus."
Besides the above hypothesis, Prof. Iwasaki also mentioned the potential relationships between COVID-19 and ACE2 receptor or HLA expression. There is no direct evidence on these assumptions, however there are several studies showing men have high levels of enzyme which is key to COVID-19 infection.  Genome‐wide association studies (GWAS) also show that HLA (human leukocyte antigen) is usually the top locus associated with infectious diseases, autoimmunity, or neurological disorders. We look forward to more research in the future to solve these mysteries to fight COVID-19.
Akiko Iwasaki and Nathan D Grubaugh, May 8 2020, “Why Does Japan Have So Few Cases of COVID-19?” EMBO Mol Med;12(5):e12481.
Uchida M et al, 2017 “Effectiveness of vaccination and wearing masks on seasonal influenza in Matsumoto City, Japan, in the 2014/2015 season: an observational study among all elementary schoolchildren.” Prev Med Rep 5: 86–91
Derek K Chu et al., June 01, 2020, “Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis”, The Lancet Journal, DOI:
B. Coper et al, April 30, 2020. “Spike mutation pipeline reveals the emergence of a more transmissible form of SARS-CoV-2” BioRxiv
Giovanni Sala, Tsuyoshi Miyakawa et al, May 17 2020, “Association of BCG vaccination policy and tuberculosis burden with incidence and mortality of COVID-19” MedRxiv
Iziah E Sama et al. May 2020 “Circulating plasma concentrations of angiotensin-converting enzyme 2 in men and women with heart failure and effects of renin–angiotensin–aldosterone inhibitors”, European Heart Journal, Volume 41, Issue 19, 14
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