Why in some countries – with the same number of infections – do we die much less from Covid than in others? Why does the US or Italy have much higher lethality rates than developing countries like Bangladesh or Nigeria? Siddhartha Mukherjee is a well-known Indian oncologist, biologist and hematologist in America, author of several essays, naturalized American and professor of medicine at Columbia University. In a long article that appeared in the New Yorker he tries to answer this simple question, starting from some personal anecdotes, which concern some cases that occurred in his country of origin.
My epidemiological whodunnit in the New Yorker this weekhttps://t.co/bXudJVpZex…. what can Agatha Christie teach us about COVID ?
— Siddhartha Mukherjee (@DrSidMukherjee) February 22, 2021
Mukherjee tells the story of Mukul Ganguly, an 83-year-old retired civil engineer who lives in Calcutta. One day, he went to the local “wet market” (like the one in Wuhan where the pandemic broke out). His family members opposed it, fearing that he would fall ill with Covid, and so – despite his precautions – the infection took place. His daughter-in-law – cousin of the author of the article in the American magazine – said that the elderly man was isolated in a room, with a pulse oximeter and an oxygen tank. For two days, Ganguly had a severe fever, then slowly recovered. Many other acquaintances of his, between the ages of seventy and eighty, have had a similar experience. None of them have known intensive care admissions.
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The New Yorker cites the testimony of a member of the Mumbai state anti Covid task force, Shashank Joshi, who reported that the intensive care units in his area are “almost empty”. This makes us think a lot: in Mumbai there is the largest shanty town in Asia, Dharavi, where a million people live in makeshift housing, the hygienic conditions are disastrous and the much-vaunted “social distancing” could never exist. When the pandemic was declared last March, epidemiologists feared that a massacre, at least three to five thousand dead, would occur in such a slum. But the feared invasion of hospitals never occurred and only a few hundred deaths have been verified, and now there are fewer and fewer deaths.
The paradox is that, usually, there are more and more victims due to infectious diseases (such as typhus, diphtheria, HIV) in developing countries. But if you look at current statistics, there are many more victims (albeit not infections) attributable to Covid-19 in rich countries such as Italy, Belgium, United States, Spain, United Kingdom, rather than poor ones. For comparison, in India – 1.3 billion population and health facilities with many problems – the deaths are one-tenth of those recorded in the United States. In Nigeria, with two hundred million inhabitants, the victims are one hundredth of those in America. Not only that: in all developing countries, especially in Asia or equatorial Africa, the lethality data are surprisingly low. Only South Africa – where the coronavirus variant is claiming many victims – is a major exception.
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What are the reasons for this difference? The New Yorker cites the demographic structure of the countries examined, which could be decisive: in a country with a very low average age, cases of Covid are necessarily less lethal. But many virologists confirm that this is only a partial explanation.
“Whatever you think of it – said to the New York magazine Mushfiq Mobarak, a Yale economist who is developing an anti-Covid strategy for developing countries – the mystery remains. Difference of ten or a hundred times is not negligible “”. In Bangladesh, where Mobarak grew up, 163 million people live, and 83,000 deaths are recorded, or 3.5 percent of Americans, for the same population. The average age, in this case, certainly matters. But this is not enough to explain certain differences. In Mexico, the average age is comparable to that of the Indian population. But India records a tenth of the deaths of those recorded in Mexico.
Mukherjee puts forward the hypothesis that too other social peculiarities must be taken into consideration. For example the structure of a typical family. Since the virus spreads between members of the same family – from grandson to grandparents – it is a fact that must be taken into due consideration. A typical household, however, decreases as the wealth of the country under consideration grows. In the United Kingdom ($ 42,000 per capita) the number is equal to 2.3 members of the same family. In Benin (income of twelve thousand dollars) it rises to 5.2, and only a fifth of these households include a person over 65.
According to Mobarak, one of the reasons for the lethality could be “the spatial distribution of the elderly”. In the US, one third of Covid deaths occurred in nursing homes and long-term residences for the elderly. But how can it be that the grandfather of a large family, with grandchildren who become easy means of contagion, is less exposed than an elderly person monitored and assisted regularly? To solve this problem, one should know the number of contacts between individuals. What is more dangerous: living in a large family but with few social contacts with the outside or in a small family unit with many social contacts?
Researchers at Imperial College London took these variables to formulate some mortality forecasts from Covid, which have proved reliable only in rich countries, but not in developing countries (at least for now: the pandemic is certainly not over). In Pakistan, 220 million inhabitants, should have mourned the deaths of 650 thousand dead, according to these models: so far twelve thousand have been registered. The Ivory Coast should have counted 52 thousand victims, but so far two hundred have been registered.
Abiola Fasina, a doctor on the front line in Lagos, Nigeria, described a situation that was far from out of control, with patients with few symptoms and constantly decreasing. Not only that: “The markets are open, and many people walk around without a mask”. According to forecasts, Nigeria should have counted between 200 and 480 thousand deaths from Covid, but so far the victims are only thirteen thousand.
Sure, many victims may not have been properly counted. Oliver Watson, an eidemiologist at Imperial College who helped create these prediction models, admits this may be the problem. “The recorded deaths from malaria are a quarter of the total,” he explains to the New Yorker. Many deaths occur at home, and there are hospitals that do not correctly count Covid deaths that occurred during hospitalization. In Zambia (which should have counted 20-30 thousand deaths) 400 victims have been counted for Covid. But it later emerged that, by verifying the causes of death of 364 deceased people, one in five had shown symptoms typical of Covid. But this is not enough to explain the discrepancy recorded.
Lack of reliable data is a serious problem. But the total death toll is more reliable. And it emerges, for example, that between May and August last year, the number of deaths in the country practically doubled. However, it is difficult to say whether this is due to Covid, or to its social effects, such as job loss, malnutrition, forced migration, shortages in the health system.
Some clues may come from the seroprevalence research. Last July, researcher Manoj Mohanan conducted a study in Karnataka, an Indian state inhabited by 64 million people. The antigenic test found that 45 percent of the people tested had had contact with the population. In New Delhi, 56%, equal to about ten million inhabitants.
Then there is the track of immunity due to T cells, a type of white blood cell that specializes in recognizing cells that are infected with viruses and are an essential part of the immune system. B lymphocytes create antibodies, while T cells “hunt” infected cells.
Both have memories of the pathogens they encountered, e they can go on the attack again. At the La Jolla Institute for Immunology in California, researchers led by Shane Crotty and Alessandro Sette studied B- and T-cell coronavirus responses in vitro, selecting plasma from donors who had never encountered the virus. Their sensational discovery was that, in approximately 40 percent of these prepandemic samples, a T-cell response occurred.
– Alessandro Sette (@SetteLab) August 2, 2020
To be sure of the result, the sample test was repeated. And it was verified that, with important differences in the population examined on a geographical basis, of 20-40 percent, the result was confirmed. Sette told the newspaper about the case of the island of Giglio, where the population was still unaffected by the pandemic. Does it have something to do with the memory of T cells, which remember something similar to the coronavirus that causes Covid? According to research currently underway, the memory of similar pathogens – such as the coronavirus that causes the common cold – could strengthen the immune response even in the presence of a new virus. And this could also explain the difference in the number of deaths in different parts of the world.
Last updated: 13:22
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