Even taking into account the differences in test tactics and calculation methods, as well as such factors as the degree of reliability and completeness of published data on the number of deaths, obvious differences in mortality rates in different countries of the world attracted the close attention of scientists who are trying to decipher the coronavirus code.
In parts of Asia, authorities quickly responded to the threat and immediately introduced a social distance regime. But researchers are studying other factors, including differences in the genetics and reactions of the immune systems, the characteristics of individual strains of the virus, the difference in levels of obesity and the health status of the population as a whole.
In China, where an outbreak of the disease occurred at the end of last year, less than 5 thousand deaths were recorded, that is, there the death rate was 3 cases per million people. In Pakistan, the figure is 6 cases per million people, in South Korea and Indonesia – five, in India – three, and in Thailand – less than one case per million. Vietnam, Cambodia and Mongolia claim that there was not a single death recorded from Sovid-19.
Now compare this to the hundred deaths per million people 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 the Japanese Chiba University have traced the path of the virus in different countries and noticed obvious differences between the regions.
“This means that we must first take into account regional differences, and only then analyze how the authorities’ policies and other factors influence the spread of infection in each particular country,” said Akihiro Hisaka from this university.
Generally accepted opinion
Currently, the initial premise is that the coronavirus – officially called SARS-CoV-2 – mutates in the same way that all viruses do, and that in one part of the world it is as infectious 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, an epidemiologist at Columbia University. – There are differences between countries in the tactics of testing, publishing data and the degree of control. There are also differences between countries in the prevalence of hypertension, chronic lung diseases, and so on.”
One of the reasons for the high mortality rate in the United States and Western Europe may have been the authorities’ reluctance to respond to an epidemic that seemed distant and relatively harmless in the initial stages. Meanwhile, in Asia, the experience of confronting the SARS and MERS epidemics prompted the authorities to quickly respond to the new threat.
Taiwan, for example, is praised for its quick response to the epidemic, including for the early screening of aircraft passengers arriving from Wuhan. The South Korean authorities have developed a large-scale program to test, track contacts and isolate patients with coronavirus.
But the relatively low mortality rate from coronavirus in Japan and India has baffled scientists. Pakistan and the Philippines have become exactly the same riddles.
Could this be explained by the characteristics of climate and culture?
A humid and hot climate could be one of the factors in Cambodia, Vietnam and Singapore. Some studies show that high air temperature and humidity can slow down – though not stop – the spread of the virus, as happens with flu viruses and other coronaviruses that cause a common cold. However, in some equatorial countries, including Ecuador and Brazil, many cases of infection and deaths due to covid-19 have been recorded.
The demographic situation also partly explains the differences between regions. For example, the younger population of Africa may have been more resilient than the older 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 a variety of habits, such as wearing masks and avoiding handshakes, helped slow the spread of the virus, and universal access to health services and an emphasis on protecting the health of older people helped reduce mortality from coronavirus.
What about different strains of the virus?
A study by a team of scientists from Cambridge University showed how the virus mutated after it left Asia and arrived in Europe. They noted that the original strain may have been “immunologically and ecologically adapted to a large segment of the East Asian population” and needed to mutate in order to overcome immune resistance outside the region.
Peter Forster, the geneticist who led the study, said there are now “extremely few clinical data” regarding how different strains of the virus interact with populations in different countries. However, he noted that the question of whether different strains of the virus could explain such different levels of mortality should be examined in detail.
A group of scientists at the Los Alamos National Laboratory also believes that a more infectious strain of coronavirus has established itself in Europe and the United States, although other experts say that the effects of various strains have not yet been studied.
“It could have been a coincidence – for example, some carriers of this mutated virus could go to rock festivals or nightclubs and transfer it to a huge number of people,” explained Jeremy Luban, a virologist at the University of Massachusetts Medical School. “However, there is also the possibility that this strain is more easily transmitted from person to person.”
Genes and immune systems
Japanese immunologist and Nobel laureate Tasuku Honjo explains that there are huge differences between Asians and Europeans in the haplotypes of human leukocyte antigens – that is, in the genes that control the immune system’s response to the virus. According to him, this may explain the lower mortality rate in Asia, but this is hardly the only reason.
Scientists from Chiba University noted that a number of possible genetic factors can determine the body’s response to the virus, and that this issue needs to be studied in detail. However, they emphasized that so far there is no evidence for this hypothesis. Differences in the responses of immune systems can also play a role.
According to Tatsuhiko Kodama of the University of Tokyo, preliminary studies show that Japanese immune systems often responded to this new coronavirus as if they were already experiencing it. He also noted that over the past few centuries, many different coronaviruses have emerged in East Asia. “The riddle of lower mortality 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 can potentially enhance immunity at the cellular level.
“Our hypothesis is that a tuberculosis vaccine plus contact with tuberculosis could have a protective effect,” said Tsuyoshi Miyakawa of Fujita Medical University.
Meanwhile, Japan is characterized by the same level of vaccination against tuberculosis as France – although different vaccines are used in these countries – but the mortality from Covid-19 is very different in them. Expert opinions are divided, but clinical trials are ongoing.
Megan Murray, an epidemiologist at Harvard Medical School, believes that scientists should also study the differences in microbiota – the trillions of bacteria that are in the intestines and play an important role in providing an immune response. “In different countries, microbiota are very different. People eat different kinds of food, ”she explained.
Obesity as one of the factors – but accident should also not be discounted.
Many Asian countries share another property, namely a much lower level of obesity among the population than in the West. Obesity is the main risk factor that determines the severe course of covid-19. In Japan, only 4% of the population is obese; in South Korea, less than 5%. Meanwhile, according to the World Health Organization, 20% or more are obese in Western Europe and 36% in the United States.
A factor such as the case, too, should not be discounted. For example, for several months it seemed that the virus had almost not affected Russia, and now it has become a powerful hotbed of a pandemic. Currently, the incidence curve in India is also creeping up, although previously it seemed that India had reached a plateau.
Epidemiologists who study coronavirus are sorely lacking in accurate data, as a result of which the initial numbers may lose their relevance with the advent of new information. According to experts, the pandemic has just begun, and solving complex scientific issues takes time.
In any case, this does not eliminate the need to remain on high alert. “Apparently, any virus that lives on our planet can kill people,” said Professor Luban of the University of Massachusetts.
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