Five months have passed since an infectious disease caused by a new coronavirus was first confirmed in Wuhan, China, late last year. While the virus has spread across the world, the number of related deaths per capita has been low in Japan and other parts of Asia. Researchers are racing to discover why.
Many people infected with the new coronavirus develop only minor symptoms, or no symptoms at all. As there are huge gaps among countries when it comes to measuring the number of infected patients, international comparisons are generally based on the per capita number of deaths from COVID-19, the disease caused by the virus.
In Japan, the number of deaths caused by the new coronavirus stood at 903 as of Tuesday, excluding those among the passengers and crew of the Diamond Princess cruise ship, which spent a high-profile period quarantined off Yokohama. Japan has experienced seven deaths per million of population, while comparable figures for countries in Europe and North America are tens of times -- or even over 100 times -- higher.
Saying that Japan has managed to contain the spread of the infections without imposing such severe restrictions as lockdowns and stay-at-home orders, Prime Minister Shinzo Abe, in lifting the state of emergency in May, stressed, "The Japanese model has demonstrated its strength."
Various factors have been pointed out as possibly linked to Japan's relative success, which include cultural ones such as a lower frequency of kissing and handshaking and beneficial customs around washing hands and wearing face masks. Also noted are such factors as the high quality of health care services, the universal health insurance plan which allows people to visit medical institutions even with mild symptoms, and the cleanliness of cities.
Yet, coronavirus deaths per capita are likewise low in China, South Korea and India. In Asian countries -- apart from Iran -- per capita deaths are nearly equal, making it difficult to attribute the small number of deaths to such factors as national characteristics and health care environments alone.
A study released in March said that in countries with a universal BCG vaccination program against tuberculosis, "there has been a tendency of lower COVID-19 cases and even lower fatalities." While the number of TB cases is small in Europe and North America, BCG immunizations have been encouraged in Asian and African countries where TB infection rates are high.
The BCG vaccine is also said to be effective in increasing the overall immune strength of a person, and there are even studies saying that inoculated children are 40% to 50% less likely to develop septicemia and non-TB respiratory infectious diseases than those who are not inoculated.
But seeming to contradict this theory is that Brazil and Iran have a high number of per capita coronavirus deaths despite having universal BCG vaccination programs, while the number of deaths is low in Australia, where a universal BCG vaccination program has not been implemented since the mid-1980s.
An Israeli study found no link between BCG vaccinations and the incidence of COVID-19.
Possible correlations with regional differences in such lifestyle-related diseases as diabetes have also been pointed out. In a study that looked at about 20,000 patients hospitalized in Britain, the risk of dying from COVID-19 was about 30% higher for obese patients than for those who were not obese.
According to the World Health Organization, many people in Europe and North America are obese, with a body mass index exceeding 30. This includes 36.2% of Americans, 27.8% of Britons and 19.9% of Italians -- compared to only 4.3% of Japanese. Yet it is hard to see that as a primary factor behind the order-of-magnitude difference in per capita deaths between Japan and those Western countries.
Also drawing attention are differences related to race or ethnicity. Eight universities and research institutes, including Keio University, launched in May a COVID-19 research group with the aim of uncovering the potentially slight genetic variations that may help divide serious cases from minor ones. The group plans to compile an interim report as early as in September.
One area eyed for such research is human leukocyte antigen (HLA). There are various HLA types, which cause different reactions in a human body to an infectious disease. For instance, a person with a certain HLA type may develop symptoms in a short period of time when infected with a human immunodeficiency virus (HIV).
Katsushi Tokunaga of the National Center for Global Health and Medicine and a member of the COVID-19 research group, said, "Cooperating internationally, we would like to compare genetic information among groups of peoples in countries in Asia, Europe, North America and elsewhere."
On the other hand, there is a phenomenon that complicates the subject of racial or ethnic genetics. According to the Centers for Disease Control and Prevention in the United States, African Americans account for 18 percent of all COVID-19 deaths in the country, even though they make up about 13 percent of the U.S. population, while Asian Americans account for 11 percent of the total deaths, while they make up 6 percent of the U.S. population. As this indicates, the number of deaths among Asian Americans and African Americans is higher in proportion to their population. Some have pointed out that income has a greater influence than race or ethnicity on COVID-19 cases and fatalities.
A new theory to explain regional differences in per capita coronavirus deaths is the idea that people in certain communities or areas have acquired a certain degree of immunity to the new coronavirus as a result of such communities or areas having experienced in the past an epidemic of a less virulent coronavirus similar to the new one.
According to research by entities such as the La Jolla Institute for Immunology in the United States, which examined blood samples collected and kept in storage before the outbreak of the new coronavirus in the United States, immune cells that recognize the new coronavirus were detected in about half of them. This is an achievement showing the possibility that cross-reactivity has occurred, triggered by a similar virus.
Seasonal coronaviruses that prevail mainly in winter only cause a minor cold, leaving research on them little advanced. If there was a large outbreak of a virus similar to the new coronavirus in Asia in the past, which helped people in the area gain a stronger immune response to the new coronavirus than people in Europe and North America, it would help explain the difference in the number of per capita coronavirus deaths.
Although full-fledged research on cross-reactivity has yet to start in Asia, there has already been a suggestive research under way.
Tatsuhiko Kodama, an emeritus professor at the University of Tokyo, and others examined blood samples of patients who had minor symptoms of the new coronavirus, and found that a certain antibody, which would ordinarily develop in the early phase of infection with a totally new pathogen, did not increase as expected. This antibody appeared in only one out of the 21 patients who, within nine to 12 days since developing symptoms, were examined by the National Institute of Infectious Diseases. This suggests that they had already gained immunity by having been infected with a different virus similar to the new coronavirus in the past, and thus their bodies did not recognize the new virus as one which they were encountering for the first time.
Regarding cross-reactivity, Prof. Masaaki Miyazawa of Kindai University, a scholar on immunology and virology, noted: "This is a plausible hypothesis. It is important to collect data related to a quantity of antibodies and cross-reactivity among regions with differences in the rate of coronavirus deaths, and make a research to compare them."
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