Some experts believe previous exposure to a similar virus helped East Asia fight COVID-19. Others are doubtful.

Dr. Yasuhiro Suzuki, who served as the highest-ranking doctor in the Japanese Ministry of Health, Labor, and Welfare's medical corps until he retired in August, told The Wall Street Journal he believes there's a "strong" theory that East Asian countries like South Korea, Japan, China, Vietnam, Taiwan, Malaysia, and Singapore have all dealt with fewer COVID-19 infections and deaths than the United States and Europe because of prior exposure to similar pathogens.

Although he acknowledged there are no studies to back up the idea, Suzuki suggested it's worth following up. "There's a theory, and I think it's quite a strong one, that in East Asia a cold similar to the novel coronavirus spread widely and a large number of people caught it," he told the Journal. "As a result of having immunity to a similar virus — although it isn't bulletproof immunity — they either don't develop it or don't get seriously ill if they do."

Dr. Tatsuhiko Kodama, who is studying coronavirus antibodies at the University of Tokyo, said that similar viruses have probably spread repeatedly in the region, and he's confident that exposure is related to the COVID-19 immune response.

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But not everyone is so sure sure that a previous virus could be behind the regional discrepancies. Prof. Tetsuya Mizutani, a virologist at the Tokyo University of Agriculture and Technology, told the Journal that the theorized pathogens would have traveled around the world just as quickly as the novel coronavirus has over the last several months. His much simpler explanation for the differences in severity? People in East Asian countries wear masks and wash their hands more consistently. Read more about research into the pandemic's regional differences at The Wall Street Journal.