(WSJ) An enduring mystery of the Covid-19 pandemic is why East Asian countries across the board have experienced far fewer cases and deaths than the U.S. and Europe.
Some doctors and scientists are beginning to take a closer look at theories that some people in East Asia and Southeast Asia have had different exposure to previous coronaviruses resembling the SARS-CoV-2 virus sweeping the globe. Such exposure could have protected them from getting sick from Covid-19 or lessened the severity of the disease.
Others doubt that the immune systems of people in the region differ from people in the rest of the world in any systematic way. They suspect cultural factors and, in some countries, government policies such as tightly enforced quarantines are playing the main role.
Whatever the case, doctors agree that some explanation is needed for why Japan, South Korea, China, Vietnam, Taiwan, Malaysia and Singapore all have experienced at most a few thousand new SARS-CoV-2 infections a day, even during the current surge. That compares with tens of thousands of daily cases in many European nations and more than 150,000 new cases on many days in the U.S.
Yasuhiro Suzuki has pondered the question as the highest-ranking doctor in the Japanese Ministry of Health, Labor and Welfare’s medical corps until his retirement in August.
“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,” Dr. Suzuki said. “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,” he said, referring to Covid-19.
He cautioned that there aren’t any solid studies to back up the idea.
Research in Western nations shows some people’s immune systems partly recognize SARS-CoV-2, the new coronavirus, even though they were never exposed to it, apparently because of previous infections by coronaviruses that cause the common cold. There are hints these people do better fending off Covid-19.
A study by scientists at the Francis Crick Institute in London and elsewhere in the U.K. looked at blood samples collected before the Covid-19 pandemic. The study, published in the journal Science, found that about one in 20 adults sampled had antibodies that recognized SARS-CoV-2, and that nearly half of children and adolescents had such antibodies.
Boston University scientists found that patients whose medical records showed confirmed exposure to common-cold viruses had better outcomes when they caught SARS-CoV-2. Among hospitalized patients, the risk of dying fell by some 70%, according to their study in the Journal of Clinical Investigation.
However, researchers haven’t compared populations across regions.
What intrigues some is the position of China as the origin not just of the current pandemic, but also of the first SARS epidemic in 2002-03 and earlier influenza epidemics. Those viruses got noticed, but others perhaps weren’t.
Tatsuhiko Kodama, who is studying SARS-CoV-2 antibodies at the University of Tokyo’s Research Center for Advanced Science and Technology, said infections with viruses resembling the new coronavirus have likely repeatedly occurred in East Asia. Dr. Kodama said he was sure that exposure was related to the immune response to SARS-CoV-2.
He said some unpublished initial data collected by his team suggest Japanese Covid-19 patients are producing a targeted antibody called IgG soon after the onset of illness while producing relatively little of another antibody called IgM that typically marks the initial immune response. This implies they have already seen something like SARS-CoV-2, he said.
However, Tetsuya Mizutani, a virologist at the Tokyo University of Agriculture and Technology, said he found it hard to imagine that earlier viruses would have stayed only in Asia, given China’s links to the world.
“Such viruses would spread around the world just as quickly as SARS-CoV-2 has done,” Prof. Mizutani said. He said cultural practices such as the high level of mask-wearing and hand-washing offered the best explanation for the regional differences in the pandemic’s severity.
Others are going farther back in history. An Australia-U.S. team recently said it found strong signs of selection among Chinese, Japanese and Vietnamese people in genes involved in combating coronaviruses. In a paper published online but not peer-reviewed, they said their analysis suggested East Asians started battling a coronavirus pandemic some 25,000 years ago and might have taken many millennia to conquer it. Another paper on a genetic risk factor for severe Covid-19 that was inherited from Neanderthals found the variant was almost absent in East Asians.
David Enard of the University of Arizona, co-author of the Australia-U.S. paper, said it was too early to know whether the changes his group detected in East Asians offered any help against SARS-CoV-2. “If there is a genetic effect, it will be small to the point of being irrelevant” compared with proven steps such as wearing masks and keeping social distance, he predicted.
Figuring out regional variation in Covid-19 immunity could come in handy in the next pandemic, Alireza Bolourian and Zahra Mojtahedi wrote in a recent commentary in Archives of Medical Research. If people in China had some pre-existing resistance to SARS-CoV-2, they said, initial data from that country could have led the West to underestimate how easily the virus could spread outside of East Asia.
In the future, they wrote, disease modelers might have to “scale up the severity of flulike epidemics” to account for that factor.
Source: Wall Street Journal by Peter Landers and Miho Inada
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