Scientists note that mortality from covid-19 in Asia was lower than in Western Europe and North America. What caused this: differences in health systems and government responses to the pandemic, or differences in the genetics of residents of these regions.
Tokyo - This has become one of the main mysteries of the coronavirus pandemic: why was the death rate from covid-19 in Asia lower than in Western Europe and North America?
Even if we take into account the differences in the tactics of conducting tests and in the methods of counting, as well as such a factor as the degree of reliability and completeness of the published data on the number of deaths, the obvious differences in mortality rates in different countries of the world have attracted close attention of scientists who are trying to decipher the coronavirus code.
In parts of Asia, authorities responded quickly to the threat and immediately imposed a social distancing regime. But researchers are looking at other factors, including differences in genetics and immune responses, the characteristics of individual strains of the virus, differences in obesity levels, and the health status of the general population.
In China, where an outbreak of the disease occurred at the end of last year, fewer than 5 thousand deaths were recorded, that is, there the death rate was 3 cases per million population. In Pakistan, the figure is 6 cases per million, in South Korea and Indonesia it is five, in India it is three, and in Thailand it is less than one case per million. Vietnam, Cambodia and Mongolia claim that no deaths from COVID-19 have been recorded there.
Now compare that to 100 deaths per million in Germany, roughly 180 in Canada, nearly 300 in the United States, and over 500 in the UK, Italy and Spain.
Scientists from Japan's Chiba University have traced the trajectory of the virus in different countries of the world and noticed obvious differences between regions.
“This means that we must first take into account regional differences, and only then analyze how the policy of the authorities and other factors affect the nature of the spread of infection in each particular country,” said Akihiro Hisaka of the university.
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Conventional wisdom
The current premise is that the coronavirus - officially called SARS-CoV-2 - mutates in the same way that all viruses do, and that it is as infectious and deadly in one part of the world as it is in another.
“We are all faced with the same virus, and we all have about the same arsenal of immune responses,” said Jeffrey Shaman, an epidemiologist at Columbia University. - There are differences between countries in testing tactics, data release and degree of control. There are also differences between countries in the prevalence of hypertension, chronic lung disease, and so on.”
One of the reasons for the high mortality rates in the United States and Western Europe may have been the reluctance of the authorities to respond to the epidemic, which at the initial stages seemed distant and relatively harmless. Meanwhile, in Asia, the experience of confronting the SARS and MERS epidemics pushed the authorities to quickly respond to the new threat.
Taiwan, for example, has been praised for its swift response to the epidemic, including screening early passengers flying from Wuhan. South Korean authorities have developed an ambitious program to test, contact tracing, and isolate coronavirus patients.
But the relatively low death rates from coronavirus in Japan and India have puzzled scientists. Pakistan and the Philippines have become the same mysteries.
Could this be explained by the peculiarities of the climate and culture?
A humid and hot climate could be a factor in Cambodia, Vietnam and Singapore. Some studies show that high air temperature and humidity can slow - although not stop - the spread of the virus, as happens with influenza viruses and other coronaviruses that cause the common cold. However, in some equatorial countries, including Ecuador and Brazil, there have been many cases of infections and deaths due to covid-19.
The demographic situation also partly explains the differences between regions. For example, the younger population in Africa may have been more resilient than the older population in northern Italy. Meanwhile, in the case of Japan, which has the oldest population in the world, scientists are looking at other factors.
It is widely believed in Japan that good personal hygiene and various habits such as wearing masks and avoiding shaking hands have helped slow the spread of the virus, and that universal access to health services and an emphasis on protecting the health of the elderly have helped reduce coronavirus deaths.
How about different strains of the virus?
A study by a team of scientists from the University of Cambridge 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 be mutated to overcome immune resistance outside the region.
Peter Forster, the geneticist who led the study, said there is "very little clinical data" right now on 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 explored in detail.
A group of scientists at Los Alamos National Laboratory also believe that a more infectious strain of coronavirus has become entrenched in Europe and the United States, although other experts say the effects of the various strains have not yet been studied.
“It could be pure coincidence - for example, some carriers of this mutated virus could go to rock festivals or nightclubs and transmit it to a huge number of people,” explained Jeremy Luban, a virologist at the University of Massachusetts School of Medicine. "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 is a huge difference between Asians and Europeans in the haplotypes of human leukocyte antigens - that is, in genes that control the immune system's response to the virus. This may explain Asia's lower death rate, he said, 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 stressed 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 reacted to this new coronavirus as if they had encountered it before. He also noted that many different coronaviruses have emerged in East Asia over the past few centuries. “The mystery of East Asia’s lower mortality rate can be explained by the presence of immunity,” he said.
Other research suggests that mass vaccination against tuberculosis may have played a role as well, because this vaccine has the potential to boost immunity at the cellular level.
“Our hypothesis is that the tuberculosis vaccine plus exposure to tuberculosis may have been protective,” said Tsuyoshi Miyakawa of Fujita Medical University.
Meanwhile, Japan has the same level of vaccination against tuberculosis as France - although these countries use different vaccines - but the deaths from Covid-19 in them are very different. Experts are divided, but clinical trials are ongoing.
Megan Murray, an epidemiologist at Harvard Medical School, believes scientists should also study the differences in microbiota - the trillions of bacteria that are found in the gut and play an important role in the immune response. “Microbiota is very different in different countries. People eat different foods,”she explained.
Obesity as one of the factors - but randomness should also not be written off
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 for 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.
Such a factor as a case, too, should not be discounted. For example, for several months it seemed that the virus had hardly affected Russia, but now it has turned into a powerful hotbed of a pandemic. Currently, the incidence curve in India is also creeping up, although earlier it seemed that India had reached a plateau.
Epidemiologists who study the coronavirus are sorely lacking accurate data, as a result of which the original figures may lose their relevance with the emergence of new information. According to experts, the pandemic has just begun, and solving complex scientific issues takes time.
In any case, this does not obviate the need to remain on high alert. “Apparently, any virus living on our planet is capable of killing people,” said Professor Luban of the University of Massachusetts.
Simon Denyer, Joel Achenbach
