Tokyo — Japan’s notable coronavirus pandemic resilience has generated scores of possible explanations, from the country’s preference for going shoeless indoors, to the purportedly low-aerosol-generating nature of Japan’s quiet conversation, to its citizens’ beneficial gut bacteria. Even irreligiousness — said to have spared the Japanese from exposure to crowded houses of worship — has been touted as a virtue in the age of COVID-19.

Despite having the world’s oldest population, with almost one in three residents 65 or older, Japan has had fewer COVID fatalities per capita than almost any other developed nation. As of Thursday, Japan had registered only 246 COVID-19 deaths per million people, surpassing even New Zealand (263) which initially adopted a zero-COVID, maximum-suppression strategy. By comparison, the U.S. has a cumulative toll of 3,045 deaths per million people.

But COVID mortality statistics alone, often based on inconsistent and/or incomplete records, don’t tell the whole story. Researchers estimate that Japan has had 111,000 “excess deaths,” more than five times the number of reported COVID fatalities, when mortality from disrupted medical care and social dislocation are factored in.

Japan’s excess mortality rate, at 44 per 100,000, far exceeds that of South Korea (4), Singapore (-15), Australia (-37), New Zealand (-9); China (0.6) and Taiwan (-5). Even less-wealthy Vietnam and Thailand fared better.

But compared to the U.S. (179) and Europe (140), Japan still comes out ahead. Some experts believe the kudos for that relative success belong first of all to the Japanese citizens, for their willingness to cooperate with antiviral measures.

“Japan’s approach to COVID response has been primarily relying on people’s effort,” not on imposing mandates, Kenji Shibuya, research director of the Tokyo Foundation for Policy Research, told CBS News. “These kinds of voluntary efforts, rather than top-down, draconian measures, did work.”

Peer pressure to wear face masks remains such a powerful force in Japan — even as heatstroke season looms — that the national Health Ministry has been compelled to issue a brochure urging people not to wear masks when they’re out walking their dogs, riding bikes, jogging or just walking to work.

In addition to nearly ubiquitous mask use, Japan’s vaccination program, which was initially delayed but then quickly implemented, is credited with saving lives. Despite initial fears about vaccine hesitancy, two-thirds of all citizens and about 90% of seniors have now received booster shots.

Japan’s generally healthy population also helped it withstand the pandemic. Lifespans have continued to expand for four decades, giving Japanese the highest average longevity on earth at 87 years for women, 81 for men. While the U.S. obesity rate ballooned to almost 42% in 2020, Japan enjoys one of the lowest obesity rates in the world, at about 4%.

Thanks in part to its universal health insurance scheme, cancer and heart disease rates are also low. Like obesity, these diseases are major underlying risk factors for complications with a coronavirus infection.

Scientists have been probing a theory, meanwhile, that Japanese people may have an inherent advantage at the cellular level when it comes to fighting off COVID. 

Researchers at the state-funded RIKEN Center for Integrative Medical Sciences have honed in on human leukocyte antigens (HLA), proteins found on most cells in all of our bodies, as a potential antiviral defense. HLA markers are well-known in the field of organ transplantation, where matching HLA types, not just blood types, is crucial to reducing the chance of organ rejection.

Riken’s study found that Japanese subjects with the HLA type A24, common here and in some other parts of Asia, develop “cross-reactive” T cells in response to seasonal coronaviruses, or common colds, which can redeploy to kill off COVID-19 infections far more quickly and effectively than in those who lack that specific marker.

Shin-ichiro Fujii, who is leading the study, told CBS News that he’s applied to run clinical trials on a vaccine aimed at immunocompromised cancer patients that would simulate the benefit of having the A24 type HLA proteins in people who are unable to develop neutralizing antibodies from the existing vaccines.

“The real hope,” he said in a statement, “is that we will be able to develop vaccines that can stimulate a strongly targeted reaction by T cells against the infection. We have demonstrated that this could be possible in this particular HLA group, but now need to look at other types.”