Tokyo — It was one of the main mysteries of the pandemic coronavirus: why mortality from covid-19 in Asia was lower than in Western Europe and North America?
Even if we consider the differences in the tactics of conducting tests and in methods of calculations, and such factors as the degree of accuracy and completeness of published data on the number of deaths, apparent differences in the levels of mortality in different countries has attracted the attention of scientists who are trying to decipher the code of the coronavirus.
In some parts of Asia the government quickly responded to the threat and immediately imposed a regime of social distancing. But researchers are studying other factors, including differences in genetics and immune systems, characteristics of individual virus strains, the difference in obesity levels and health status of the population as a whole.
In China, where at the end of last year, an outbreak of this disease, there were less than 5 thousand deaths, that is, there the mortality rate was 3 cases per million population. In Pakistan, the average is 6 cases per million population in South Korea and Indonesia — five in India — three in Thailand — less than one in a million. Vietnam, Cambodia and Mongolia argue that there has not been a single death from сovid-19.
Now compare this with a hundred deaths per million population in Germany, about 180 cases in Canada, nearly 300 cases in the United States and more than 500 cases in the UK, Italy and Spain.
Scientists from Japanese University of Chiba drew a trajectory of exposure to the virus in different countries and noticed obvious differences between the regions.
“This means that first of all we should take into account regional differences, and then analyze how government policies and other factors affecting the pattern of infection in each country,” said Akihiro Hisaka (Akihiro Hisaka) from this University.
Conventional wisdom
Currently, the premise is to ensure that the coronavirus — officially called SARS-CoV-2 — mutates as well, as do all viruses, and in one part of the world it is as contagious and deadly as in the other.
“We all face the same virus, and we all have roughly the same Arsenal of immune responses, said Jeffrey Shaman (Jeffrey Shaman), an epidemiologist from Columbia University. Between countries there are differences in the tactics of testing, the publication of data and degree of control. Between countries there are also differences in the prevalence of hypertension, chronic lung disease and so forth.”
One of the reasons for high mortality rate in the United States and Western Europe may have been the unwillingness of the authorities to respond to the epidemic, which in the initial stages seemed distant and relatively harmless. Meanwhile in Asia, the experience of fighting the epidemic SARS and MERS has pushed the authorities to respond quickly to the new threat.
Taiwan, for example, praised for fast response to the epidemic, including early screening passengers of airplanes arriving from Wuhan. The South Korean authorities have developed an ambitious programme of testing, contact tracing and isolation of patients with coronavirus.
But the relatively low rate of deaths from coronavirus in Japan and India put scientists in a deadlock. The same mysteries have become Pakistan and the Philippines.
Could this be explained by the peculiarities of climate and culture?
Humid and hot climate could be a factor in Cambodia, Vietnam and Singapore. Some studies show that high temperatures and humidity can slow — but not stop — the spread of the virus, as happens with influenza virus and other coronaviruses that cause the common cold. However, in some Equatorial countries, including Ecuador and Brazil, there were a lot of infections and deaths due covid-19.
The demographic situation also partly explains the differences between the regions. For example, a young population of Africa may be more sustainable than a more elderly population of Northern Italy. Meanwhile, in the case of Japan, which is characterized by the oldest population in the world, scientists are studying other factors.
In Japan it is widely believed that good personal hygiene and different habits such as the wearing of masks and avoidance of handshakes, helped to slow the spread of the virus, and the system of universal access to health care and the emphasis on the protection of the health of older people helped to reduce deaths from coronavirus.
How about different strains of the virus?
A study conducted by a team of scientists from Cambridge University, showed how the virus mutated after he left Asia and arrived in Europe. They noted that the initial strain may have been “in immunological and environmental sense, adapted to a large segment of the population in East Asia,” and he had to mutate to overcome immune resistance outside this region.
Peter Forster (Peter Forster), a geneticist who led the study, said that “very little clinical data” regarding how different strains interact with people of different countries. However, he noted that it is necessary to study in detail the question of whether different strains of the virus to explain such different levels of mortality.
A group of scientists at the National laboratory Los Alamos, too, believes that in Europe and the United States have established a more contagious strain of coronavirus, although other experts say that the influence of the different strains is not yet understood.
“It could be pure coincidence — for example, some carriers of this mutated virus could go to rock festivals or in night clubs and pass it to a huge number of people explained Jeremy Luban (Jeremy Luban), a virologist from the Medical school at the University of Massachusetts. — However, there is also the possibility that this strain is more easily transmitted from person to person”.
Genes and immune system
Japanese immunologist and Nobel laureate Tasuku Honjo (Honjo Tasuku) explains that between Asians and Europeans there is a huge difference in the haplotypes human leukocyte antigens — that is, in genes that control the immune system’s response to the virus. According to him, this may explain a lower mortality rate in Asia, however, this is hardly the only reason.
Scientists from Chiba University have noted that a number of possible genetic factors can determine the body’s response to the virus, and that this issue should be explored in detail. However, they stressed that so far evidence for this hypothesis is not. Differences of reactions in the immune systems can also play a role.
According to Tatsuhiko Kodama (Kodama Tatsuhiko) from the University of Tokyo, the results of preliminary studies show that the immune system of Japanese often react to this new coronavirus as if they have already encountered him. He also noted that over the last few centuries in East Asia there were many different coronaviruses. “The mystery of the lower mortality rate in East Asia can be explained by the presence of immunity,” he said.
Other studies show that mass vaccination against tuberculosis could also play a role, because this vaccine has the potential to strengthen the immune system at the cellular level.
“Our hypothesis is that a vaccine against tuberculosis plus contacts with tuberculosis could have a protective effect,” said Cueshe Miyakawa (Tsuyoshi Miyakawa) from the Medical University Fujita.
Meanwhile, Japan’s typical for the same level of vaccination against tuberculosis, as in France — although in these countries use different vaccines, but the deaths from Covid-19 in them is very different. Opinions of experts were divided, but clinical trials are ongoing.
Megan Murray (Megan Murray), an epidemiologist from the Harvard Medical school, believes that scientists should also study the differences in microbiota — the trillions of bacteria that reside in the intestine and play an important role in providing immune responses. “In different countries of the microbiota is very different. People eat different food,” she explained.
Obesity is one of the factors — but an accident is not worth it to write off
Many Asian countries share another property, namely a much lower level of obesity than in the West. Obesity is a major risk factor that determines severe covid-19. In Japan obese and only 4% of the population in South Korea is less than 5%. Meanwhile, according to the world health organization, in Western Europe, obesity affects 20% or more in the United States — 36%.
Such factors as occasion, too, should not be discounted. For example, for several months it seemed that the virus is almost not affected Russia, and now it has evolved into a powerful center of the pandemic. Currently, the incidence curve in India is also creeping up, although previously it seemed that India came out on the plateau.
Epidemiologists who investigate the coronavirus is a severe lack of accurate data, with the result that the initial figures may lose its relevance with the emergence of new information. According to experts, the pandemic has just begun, and the solution of complex scientific issues requires time.
In any case, this does not negate the need to stay in the mode of increased readiness. “Apparently, any virus living on our planet, capable of killing people,” said Professor Luban from the University of Massachusetts.
