Regional Immunity? Why Asia Has Avoided The Worst Of COVID-19
East Asia is home to 30% of the world's population but has recorded only 2.4% of the COVID-19 global death toll. Scientists are looking at possible immunity from past epidemics or even genetics.
TOKYO — This is one of the great mysteries of the COVID-19 pandemic. Countries in East Asia were affected by the spread of the virus several weeks before Europe and the United States and yet they were notably able to get through the health crisis and to disclose, despite several waves of infection, much lower death tolls than those in the West.
Cumulatively, the ten members of ASEAN (Indonesia, Malaysia, the Philippines, Singapore, Thailand, Brunei, Vietnam, Laos, Myanmar and Cambodia) and the developed countries of North-East Asia (China, Japan, South Korea and Taiwan) have recorded only 44,000 deaths linked to COVID-19 since January 2020, i.e. barely ... 2.4% of the 1.8 million fatalities worldwide. This is fewer than the 65,000 deaths recorded in France. To put this in perspective, with 2.3 billion inhabitants, East Asia is home to 30% of the entire world population.
Regardless of their level of development or the strength of their state, all the territories in the region have recorded an extremely low number of deaths per million inhabitants. The ratio is 0.36 in Vietnam, 0.29 in Taiwan and 3.4 in China. Cambodia and Laos haven't identified a single victim in 11 months. By way of comparison, France"s death toll is 970 per one million inhabitants and the United States' has reached 1,034.
Japan and South Korea have been facing an acceleration in the number of infections since November, but it remains a very limited number of cases. On one of its "worst" days, Dec. 31, Japan identified 4,520 positive cases for 126 million people while on Dec. 20, South Korea broke its record with 1,097 positive tests in 24 hours. At the beginning of January, these two countries had recorded a total of 4,284 deaths since the start of the pandemic — less than what the United States recently mourned in a single day.
In the last months, these gigantic gaps between Asia and the rest of the world have generated an avalanche of talk about the "incompetence" or "effectiveness' of various governments, while others described an improbable "discipline" or a "cultural particularism" of the populations of the East. Some television analysts even mocked the supposed "authoritarianism" of the Asian capitals such as Beijing, which would have "policed" or "locked up" their "docile" populations. And yet, in reality, many countries in the region have survived the crisis without ever violating the fundamental freedoms of their citizens.
In Japan, no restriction has been imposed on the population. In South Korea, no restriction of movement has been implemented nationwide. Taiwan hasn't decreed a lockdown either.
If experts want to dismiss this idea of an "Asian character" which would magically explain the region's low tolls, they point to some political features that these countries share.
Across the continent, people were quick to adopt mask-wearing without question, as wearing this protective gear was already common practice in Japan and South Korea. "The big differences with the West have been the strict border shutdowns and the rigorous testing of infected people, whether they were sick or asymptomatic," notes Professor Teo Yik Ying, dean of the Saw Swee Hock School of Public Health at the National University of Singapore.
In order to stop the spread of the virus, governments in the region all isolated themselves from the world before March. People who were able to enter these countries had to follow very strict quarantine rules and undergo tests both at the beginning and at the end of their isolation phase.
Following a similar rule, infected but healthy inhabitants also had to stay in hotels or accommodation controlled by public authorities for at least two weeks. "It was crucial to take them out of the community to avoid the spread of the virus within families," says Teo Yik Ying.
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In the countries that did implement strict lockdowns, such as China and Myanmar, authorities only gave their "freedom" back to citizens when no new case was detected for several days in a row. "In Europe, countries are reopening although they still have thousands of new infections every day. It can't work," says the expert.
While they confirm the weight of these socio-political factors, scientists are still astonished by the exceptional performance of Asia and are now reflecting upon a more medical explanation. What if Asian populations were naturally more resistant to the coronavirus? Could there be some form of "Asian immunity" linked to past epidemics or even genetic characteristics?
In Tokyo, a number of researchers are convinced of the validity of these hypotheses. To try to confirm them, Tatsuhiko Kodama, of the University of Tokyo, has analyzed the immune response of more than 100 people infected with the coronavirus in Japan these past few months. He was surprised to discover the high level of a particular type of antibody in the blood of all his patients.
Across the continent, people were quick to adopt mask-wearing without question — Photo: Xinhua via ZUMA Press
Usually, when a patient is attacked by an unknown foreign substance, his immune system will first generate an antibody called "IgM" to defend itself against the virus. A few days later, when his immune system has integrated this first attack and started to build an immune memory, he will generate a second type of antibody called "IgG".
"However, our patients, who were infected with SARS-CoV-2, immediately show high levels of IgG antibodies and low levels of IgM", explains Tatsuhiko Kodama. "So we deduced that their system reacts as if it had already been attacked in the past by a coronavirus of the same type."
According to the researcher, East Asia populations have therefore naturally developed a form of resistance to SARS-CoV-2. This is because they have already been exposed, over the course of their lives, to a multitude of other less ferocious cousins of the coronavirus. "It's not just MERS or SARS, but many other viruses of a similar type which are circulating," he says. "This explains why the death toll is so low in East Asia."
Carrying this reasoning one step further, other Japanese experts are wondering if this exposure to past epidemics over the course of thousands of years may have generated genetic differences between the inhabitants of Asia and other populations in the rest of the world.
A "Coronavirus Task Force" gathering several universities in the Archipelago thus recovered the data of 500 people who were infected with COVID-19. The team divided this representative sample into two groups: One with people who have developed very serious symptoms and the other with patients who have only experienced very mild symptoms.
The researchers then organized the sequencing of the genomes of all these 500 positive cases. They then compared some of the genes which are involved in the development of a response to the attack of the virus and analyzed the type of the "HLA" of each patient. This group of molecules, which is located on the surface of cells, acts as the control tower of the immune system and is very different from one person to another.
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"They are very different in Asians and Caucasians," points out Tasuku Honjo, an immunotherapy specialist who won the Nobel Prize in medicine in 2018. "Yet this group of molecules plays a very important role in the identification of a pathogenic agent." If the Japanese team hasn't yet delivered its conclusions, it thinks it will be able in the coming months to shed some light on the racial factors involved in patients' reactions to the SARS-CoV-2 infection.
For decades, researchers have identified differences in how populations around the world react to certain infectious diseases. "For example, Africans are better protected than Europeans against some types of malaria," argues Lluis Quintana-Murci, population geneticist at the Institut Pasteur and professor at the Collège de France. "Due to natural selection, they have different genetic defense mechanisms," explains the scientist, who adds that current populations, on each continent, descend from multiple generations who have survived past epidemics.
A recent study carried out among the inhabitants of Cape Verde, an island group off the coast of Senegal, has shown that a genetic variant allowing increased resistance to malaria had become common in the population, since Portuguese sailors first established themselves there with African slaves 500 years ago. Half of the inhabitants of the islands now carry a gene variant which helps reduce the amount of receptors that the parasites use to enter the sick person's cells. "Some resistance factors can be part of our genes," Lluis Quintana-Murci says.
Although compelling, this genetic explanation isn't enough in the case of COVID-19, specialists admit. "In order to replicate, viruses must interact with hundreds of genes in the human genome," confirms David Enard of the University of Arizona. The researcher has recently co-authored a large American-Australian study which highlights a relative enrichment of around forty genes which have interacted with coronaviruses in populations of East Asia.
His teams believe that a natural selection, which was triggered 25,000 years ago by a large regional outbreak, caused these changes in East Asia's genetic structures. These modifications aren't present in the genes of populations from other continents. "But we can't conclude that there is a strong difference. These altered genes have very little effect in the whole process. We don't have proof yet of an Asian genetic immunity to COVID-19," insists Enard, who prefers the explanation of an immunity memory that certain populations who have already been exposed to other viruses could have developed.
The researcher hopes that these findings won't be politically misdirected to question the rules of social distancing or the wearing of masks, which have proven to be effective worldwide. "In the end, it will take years of research before we are really able to understand this pandemic," he says.