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While early studies of who was dying of Covid-19 identified risks such as obesity and having diabetes, there is a growing realization that those initial conclusions might have been misleading, obscuring a more significant explanation.

As researchers pull back their lens from individuals to population-level risk factors, they’re finding that, in the U.S., race may be as important as age in gauging a person’s likelihood of dying from the disease.

The higher the percentage of Black residents in a county, the higher its death rate from Covid-19 — even after accounting for income, health insurance coverage, rates of diabetes and obesity, and public transit use, finds a new study by researchers at the MIT Sloan School of Management. With those plausible explanations ruled out, “the causal mechanism has to be something else,” said applied economist Chris Knittel, the study’s senior author. “If I were a public official, I’d be looking at differences in the quality of insurance, conditions such as chronic stress, and systemic discrimination.”


The county-by-county analysis of Covid-19 death rates in the U.S. comes as more and more studies shift from the initial focus on individual-level factors that seem to increase people’s risk of dying to population-level ones, too, said experts in public health, demographics, and infectious disease.

One reason for the new focus is that “we’re not learning much more beyond what’s been observed from the start of the pandemic: that sex, age, and preexisting conditions put you at greater risk of dying” from Covid-19, said Aaron Glatt, an infectious disease physician at the Icahn School of Medicine at Mount Sinai. In almost every country, for instance, more men than women are dying of Covid-19, an imbalance that likely reflects both biology — women have stronger immune systems — and socialization: They seem to be following social distancing guidelines more than men, which could decrease the viral load they’re exposed to.


Also driving the shift in focus is that society-level influences are potentially more “actionable” than individual risk factors; you can’t change your blood type. A study posted to the preprint site medRxiv this month reported that type O is associated with lower risk of respiratory failure from Covid-19 and type A with a higher risk, but the paper hasn’t been peer-reviewed and it’s not clear how much difference blood type might make. “I wouldn’t tell one patient, thank God you have type O, but another, start preparing your will because you’re type A,” Glatt said.

To investigate population-level factors, MIT’s Knittel and graduate student Bora Ozaltun analyzed county-by-county mortality rates — the number of deaths from Covid-19 as a percentage of population, from April 4 to May 27. The mortality rate is more precise than the infection rate or the case fatality rate (the percent of diagnosed cases who die), which are imprecise because of inadequate testing. In contrast, although some Covid-19 deaths were incorrectly attributed to other causes, especially early in the U.S. outbreak, “deaths, sadly, are an absolute,” Knittel said.

They then used standard statistical tools to tease out which factors are most strongly correlated with mortality rates. Race stood out. Nationwide, the average county-level death rate from Covid-19 is 12 per 100,000 people. Counties with a Black population above 85% had a death rate up to 10 times higher. For every 10 percentage point increase in a county’s Black population, its Covid-19 death rate roughly doubles, Knittel said.

That meshes with other research. A study last month of 1,052 Covid-19 patients treated at Sutter Health hospitals in California, for instance, found that Black patients had 2.7 times the odds of hospitalization as non-Hispanic white patients, indicating more severe disease. And an analysis by scientists at the Harvard T.H. Chan School of Public Health found that the death rate in predominantly non-white areas is six times that in non-Hispanic white areas.

“Black people are dying of Covid-19 at a rate more than twice our share of the population,” said Malika Fair, an emergency medicine physician in Washington, D.C., and senior director of health equity programs at the Association of American Medical Colleges.

The MIT researchers’ key finding is that the underlying reasons for the link between race and death rate are not the usual suspects.

“Policymakers’ natural instinct is to think this correlation is because of income disparities, or having health insurance, or diabetes, obesity rates, smoking rates, or even use of public transit,” Knittel said. “It’s not. We controlled for all of those. The reason why [Black people] face higher death rates is not because they have higher rates of uninsured, poverty, diabetes, or these other factors.”

The Sutter study, too, adjusted for age, sex, comorbidities, and income; the higher hospitalization rate for Black patients wasn’t explained by any of those.

That leaves other factors. “If I were a policymaker,” Knittel said, “I’d be looking at things like the systemic racism that affects the quality of insurance African Americans have and the quality of the health care they receive.”

People with Medicaid or high-deductible plans, for instance, are less likely to have a primary care physician; 34% of Black people and 15% of white individuals are covered by Medicaid and therefore less likely than people with employer-sponsored insurance to have a regular physician.

“People who didn’t have a relationship with a primary care provider were much less likely to get tested,” said Georges Benjamin, a physician and executive director of the American Public Health Association. “Testing sites were put in affluent communities, or required a car, and testing kits were in short supply. Any time there is a shortage of something, minorities are less likely to get it.”

Without a primary care provider, Black people who thought they were infected were also likely to be turned away from hospitals, Benjamin said. “Someone without a primary care doctor doesn’t get into the ER as fast as someone whose doctor calls ahead,” he said. “At what point were your symptoms severe enough that you got into the health care system?” For people of color, it was likely later, he suggests.

“Black patients presenting with fever and cough were less likely to receive a referral for a Covid-19 test,” Fair said. That delayed appropriate care.

And once they do get into the system, research has found, the quality of care Black people receive for a variety of conditions, such as cardiovascular disease, is likely to be lower. Racism “is apparent in how we treat patients,” Fair said. “We still see differences in the care [for many conditions] given to Blacks and whites.”

Another possible factor in the high death rate among Black Americans is the well-documented health effects, including on the immune system, of chronic stress such as that caused by a lifetime of discrimination.

In the MIT study, the correlation between a county’s Covid-19 death rate and its proportion of Black residents was stronger within any given state than between states. “That tells me that there are important state-level differences that drive these deaths,” Knittel said. “African Americans are more likely to live in states with poor health care systems.”

Commuting via public transportation, relative to telecommuting, is also linked to a higher death rate. When public transit use is 20.6 percentage points higher in one county than another, its death rate is about tenfold higher.

Driving to work was also linked to a higher death rate. Many people working at their place of employment rather than home were in public-facing and therefore risky occupations such as health care, grocery stores, and public safety. “The correlation between death rate and driving to work suggests that just being at work, no matter how you get there, increases your risk of dying,” Knittel said.

Those positions are also filled disproportionately with people of color, likely contributing to the correlation between race and death rates. “Clearly, people who have jobs where they come into contact with others, from health care workers to bus drivers, are more likely to become infected,” the APHA’s Benjamin said. Although much about the pathology of the new coronavirus remains a mystery, the chance of becoming infected is partly a function of how much virus one is exposed to; the more infected people someone encounters, the higher that viral load can be.

The new population-level approach to understanding risk has prompted a rethinking of the role of conditions such as obesity and type 2 diabetes.

“Obesity is a marker of poverty and therefore of access to high-quality health care,” said Nina Schwalbe of the Mailman School of Public Health at Columbia University. Although the physiological consequences of obesity, notably high rates of inflammation, might contribute to Covid-19 severity, “obesity is a signal for so many of the social determinants of health, and we have to ask what this signal is telling us about vulnerabilities,” Schwalbe said.

That holds for type 2 diabetes as well. An analysis of 13 separate studies found that the disease is associated with 3.7 times the risk of having severe Covid-19 or dying from it compared to not having any underlying illness. This, too, is a disease of poverty, which means those who have it are more likely to live in crowded homes where “social distancing” is impossible, more likely not to have a primary care physician, and more likely to have jobs that increase their exposure to infected people.

The Sutter and MIT studies cast doubt on whether individual risk factors are as important as social determinants of health in affecting someone’s chances of contracting severe and even fatal Covid-19. “It should cause us to ask a different set of questions about what puts you at risk of hospitalization or death,” Schwalbe said.

More and more evidence is pointing to social determinants of risk, which puts the role of underlying health conditions in a new light. “Comorbidities are still used to blame people for how hard they are hit by Covid-19,” said Philip Alberti, senior director for health equity research at the AAMC. To reduce the U.S. death toll now that many states are seeing a new surge in cases, he said, “our response to this disease” must look beyond the strictly medical.

  • “They [women] seem to be following social distancing guidelines more than men, which could decrease the viral load they’re exposed to.” This– the behavior of those with higher mortality rates might be part of the cause –seems like a hypothesis that ought to be explored. But with anything having to do with race, similar lines of speculation are completely taboo. We must never never examine hypotheses that might produce an answer contrary to the everything-must-be-explained-in-a victim/oppressor-paradigm. So possible solutions, such as changing behavior in categories with higher fatality rates, cannot be explored, even though it might reduce the death rates.

  • I can not understand the paper, the summary is in English but without substantial background I do not think it is enough to explain it, but there is a paper out by some Italian researchers which says due to lower rates of ACE2 expression, black people should in theory be less like to catch coronavirus – (I know there are many coronavirae but I am not using “Covid 19” when that is an unnatural name the Chinese govt. got WHO to come up with to avoid calling it “Wuhan” as it ought to be)
    But they also concluded, this is the part I do not get, that once they have it, it could be worse for them – also due to lower ACE2, that is where they lost me.

    Anyway, that paper seeks to answer this question. Use a search engine for coronavirus black ACE2, it should come up.

    I have no idea if black health care is inferior to white, but it seems to me, I do not want anyone going to the explanation of “stress” unless they have exhausted everything else – PARTICULARLY if I was black, because what can you do about “stress” as the clinician who is treating me? But if there is an actual cause, a reason I am doing worse as a black man, maybe the doctors can help?

  • Are they also looking at diseases that are more prevalent in the black community than in non-black (e.g., Sickle Cell). While systemic racism could play a role, it would be critical to double check that there isn’t some biological reason involved, that there isn’t a social factor involved and then if all that is left is systemic racism, it needs to be specific so that it can be acted upon and results measured.

  • The study looks at all the usual social factors (income etc.) and finds they do not explain the disparity, so instead of, like true scientists, acknowledging that their study does not provide an answer, they supply an answer that is not supported by their study or data. One of their unsupported explanations is “stress”, that all purpose, nebulous, can’t-really-define-it buzzword. Must be pure coincidence that their speculations advertise their virtuous social beliefs.

  • Quit the race-baiting. Because you have Medicaid is no excuse not to have a primary care physician. “Chronic discrimination”, “systemic racism”. Please quit publishing crap like this. Might they be more genetically susceptible as at least a possibility. Is this a covert promotion of Medicare for all. If it is, the US if you account for population, has a lower death rate than all of the so-called western democracies of Europe with the exception of Germany.

    • We have one of the most bloated, ineffective health systems in the world and are not even in the top 10 for health outcomes. Pretend you have Medicaid and call your favorite providers and see if they will take your insurance….this isn’t race baiting, the death rates are real and the conversation of why this is occurring needs to happen now. Try listening.

    • A lot of sensible comments. There are racial differences which are nothing to do with racism. As many have said blacks need to help themselves. Keep race issues out of these discussions

    • Leslie – I do not really have an opinion about how bad Medicare is – if it is bad at all – but it seems to me you did not refute the point about many countries in Europe doing worse than the US – (so FAR, that is – I am not making any bets it will stay that way).

      I do not know what is going on, but the the other poster who pointed out those who did the study are speculating about “stress” seems right on point.

      The way the study is presented by this article, is deaths correlate highly with percentage of black population – but they did not mention infection rates – they seem eager to jump to inferior health care as an explanation but the entire study seems flawed that way – do a study where you determine infection rate in different “races” – then see if they died at the same rates, to see if there was a difference in outcome after infection was confirmed.
      Even then, you would not be eliminating different genetic vulnerability as a cause.

    • The US has the 9th highest per capita death rate in the world. As for universal health care, all other “western democracies” have it, along with better COVID figures.

    • pd – the US has not done great – in my view, we should have gone to some kind of government care, at the least, for this disease -but the claim we have done worse than all the “Western Democracies” I am not accurate from what I read – I think Italy, Spain, Sweden, and maybe Great Britain have done worse so far. Is that wrong?

    • Pd -I think the US has a lower rate than Sweden, Italy and Spain – and maybe Great Britain- given time, we may well do worse – I think we will – but right now, not as bad if what I read online is right.

  • I believe the article states that eliminating the usual variables such as poverty, poor health care etc. there still appears to be a racial vulnerability to Covid19. The article then seems to ignore that data and return to the racism angle. Just as men are more vulnerable than women,old are more vulnerable than young, a focus on racial predispositions should be done,as it is for many diseases.

  • As an African American with over 20 years of public health experience (primarily in infectious disease) I can attest to the overt racist practices of the majority of non Black health care providers I’ve encountered. There is no rationalizing away the poor health outcomes of Black people. The ‘systems’ are inherently racist. Our nation was founded, and still stands, on the ultimate success of systemic racism.

    • Christina, completely agree. As usual, a random white man has chimed in that it’s all Black people’s fault and to look within. That’s crazy! It’s more convenient for someone in power to point fingers at those who are not and deny they created the power structure that they benefit from…but it’s so obviously untrue. A lot of us are against “how things are” and will work for inclusion and equality, and continue the work to recognize and correct the inequities we as white people have benefitted from at the expense of brown and black people.

      Colin: grow up, please!

    • Well you hit all of the talking points at least. I notice they there is a lot of talk about this ‘power structure’ but no hard evidence that it even exists.

      I’ve seen the cherry picked lists that describe ‘white male privilege’. And I remember the time I was a soldier who applied for the West Point preparatory school. This was back in the days before they were pretending to be fair and I was told that I was the most qualified applicant – but since there were a sufficient number of qualified minorities – I was not selected.

      Ever notice that the only group who does not have a scholarships that are only for that demographic are white males?

      Is this ‘privilege’?’ I was so privilege’d that I had to join the military in order to get the money to attend college. And after that it was my privelage to get a BBA, a BS and a Master’s while holding down a full time job or on active duty in the military.

      I also had the privelage of being the victim of a false sexual misconduct complaint. She didn’t have anything against me personally – but she suspected that her name was on the layoff list (it was) and knew that if she made such a complaint she would be layoff proof. And her name was taken of the list for that specific reason. The company would have won the lawsuit but it would have been expensive and their name would be dragged through the mud. But they had a problem – they did not want me talking about what had happenned. So they made me sign an NDA about the whole incident in order to keep my job. (Because if they let me go – I would not be able to say anything or else the company would say that I was released after a sexual misconduct complaint.)

      Sorry – this is ‘privilege” and ‘systemic racism’ is BS. Because without the excuse of ‘racism’ people would have to be responsible for the choices they make in life.

      Nobody. Ever. Gave. Me. Anything.

    • I have to try to reason with you about “Our nation was founded, and still stand on the ultimate success of systemic racism”

      Please try to think this through – sure, there was slavery in the US – only in some states – from the beginning – but New England was prosperous from the early days of this country – no slavery in New England – pretty much no black people until after World War 1 – by which time, America was a major world power, and pretty wealthy. I do not mean to say black people did not help build America, but there is no reason to think the wealth and success of American came from the exploitation of black people. It really did not, there is no historical basis for that claim.
      And, likewise, black people having less money now than white people, overall, does not benefit white people – this idea is the cause of a lot of resentment which is totally misplaced.
      Until fairly recently, mostly after American began to decline, the white population was maybe 85% of the total – did the other 15% of the population, the non- white 15%, carry all the rest of us, do nearly all the work, to become the preeminent world power, win two world wars, get about 1/2 the world’s trade, during the period of say the 1950s to 1970s?
      That is simply impossible.
      With no slavery and no black population at all, the evidence is pretty strong America would have pretty much the same history.

  • It beggars belief that the authors have not considered the measurement of simple parameters such as population average nutritional parameters such as vitamin D, A and C levels or the levels of zinc magnesium and selenium

    All these – and others – have a role in innate immune response to viral infection

    It perhaps betrays a subconscious ol/ or even overt – political bias – to find reasons to blame white racial prejudice for the response differences or, like the persistent trials of hydroxychloroquine in the wrong population ( in hospitalised, hyperinflammation suffering patients rather than early in the disease which was the stage In which first positive reports of large case reports – and without zinc to boot) as perhaps a way of discrediting the current president.

    If this surmise is correct, one can just shake ones head in incredulity ..

    • Well said John. The critical role of ionophores for Zn (including but not limited to hydroxychloroquine), despite extensive research on its inhibition of viral replicase and actions at the ACE2 receptors, is a serious omission. Especially considering that moderate Zn deficiency is most prevalent in the elderly, African Americans, and Hispanics. Likewise, the correlation of low D3 with corona virus severity and it’s prevalence in the elderly, obese, DM2, African Americans and Hispanics. Where I am, there is a large multi-ethnic work force. They all have the same insurance. The hospital director is African American as are 2 of the pulmonologists. The pattern of mortality persists. Yet the science is ignored for the sake of politics.

  • Why do you blame racism for everything? Who prevented the Medicaid holder from having a relationship with a primary care provider? Who is responsible for obesity? Sorry, I have enough of my own responsibilities without feeling guilty about someone not caring about their own responsibilities. Race may be a relevant factor in COVID-19 mortality, but Racism is not.

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