Skip to Main Content

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.

  • The fact you failed to mention VITAMIN D DEFICIENCY in darker pigmented populations – ceteris paribus with equally situated (geographically and socioeconomically) non-blacks – borders on CRIMINAL NEGLIGANCE.

    And UNTIL you “explore” THOSE types of factors – KNOWN variances within basic biology, that are (again) KNOWN to increase risk among darker-skinned folks for decades – the evidence being lighter skin itself, with all it’s downsides in terms of skin cancer, etc – you can NOT be taken seriously as a “scientist” but only viewed with disdain as a POLITICAL writer.

    I know I’m echoing things said elsewhere in the comments – and ONLY in the comments. But I have been part of an effort by BCBS to GET THIS MESSAGE OUT regarding Vitamin D deficiency AND THIS TYPE OF ARTICLE IS DROWNING OUR MESSAGE.

    Resulting in DEATH – yeah, Death – for some who might have survived otherwise. Given the rates of infection, that statement can be made p<.01.

    STOP IT. PLEASE. This isn't a game. Thank you.

  • What would improve the quality of this article is to remove the inherent bias made transparent by the use of “Black” everywhere the term should be black. This is an article intended to flame racial tension and ignores the fundamental principles needed to evaluate data critically without a presupposed outcome. Shame on you for publishing this garbage.

  • It’s clear that people living in poverty in the US have worse COVID outcomes than more wealthy individuals (for a variety of reasons). It’s also clear that Afro Americans are more likely to be poor than white Americans (for a variety of reasons). Does that mean that the US health system is racist? I don’t think so. What it does mean is that poor people in the USA are under-served by the health system. Does anyone still think it’s OK that people have to make personal medical health care decisions based on if they can afford it or not?

    • A quick test of the level of “racism” in the US Health System – compare it to the UK, where the NHS is run by government, “equal access” to all (in theory).

      OK, so the same racial disparity exists there. Hmmm … blows a hole in the “RACISM” screeds … never mind, issue more Screeds…! Quantity having a quality all its own, eh. UGH.

      I’ll incorporate by reference my other comment on Vitamin D, rather than repeat it here. Argh.

  • How about the fact that they have darker skin? Why not start with the most obvious reason? It has been shown in a study out of a New Orleans ICU, that 100 percent of the patients with Covid in the ICU under the age of 75 had proven vitamin D insufficiency. Because of their darker skin color, it takes African-Americans over 6 times as long to obtain the same amount of vitamin D from sunlight as a fair-skinned individual. A fair-skinned person living below the 37th parallel can synthesize enough vitamin D from sunlight in about 15-20 minutes. It takes a darker-skinned individual 90 minutes or more. This is also why people in nursing homes and obese people were more susceptible to negative outcomes. People living in nursing homes do not get adequate sunshine and your ability to synthesize vitamin D from sunlight decreases exponentially as you age. Obese populations also do not synthesize vitamin D as similar rates to healthier populations. This is also why there were more deaths among people of Indian ancestry in the UK and Native American populations in the United States. The science of nutrition and nutritional deficiencies has almost completely died because of big pharma and their never-ending search for new drugs to treat the symptoms of disease instead of actually curing it.

    • To assume a causal relationship between skin color or Vit. D absorption and susceptibility to Covid-19 or vulnerability to its effects is ridiculous. Correlation does not mean causation- one of the basic tenets of scientific process! Please be ware of the fumes of pseudo science in all this Corona Miasma!

    • Elliot don’t be a nincompoop and ASSUME there’s no correlation – why don’t you google the relationships established between Vitamin D deficiency and infectious disease, immune health, even cancer.

      Then revise. We all make mistakes, eh. The right thing to do is revise.

    • Here’s an example – I made a mistake by typing “correlation” and should have said “physiological causality leading to correlation” or something similar.

      Mea culpa. See … it’s not that hard.

    • It seems so much easier to blame systemic racism than obvious biological differences. I think it is bizarre that it has comet to this. Lack of curiosity and blaming the wrong problem are going to increase death. I am fully aware of the difference between correlation and causation, but the correlation is high and that is why it is worth noting. Duh! Elderly populations are dying at a higher rate, too. This is because they also have a harder time synthesizing vitamin D and are less active.
      “Several clinical trials and pooled studies show that vitamin D supplementation lowers the odds of developing an acute respiratory infection by 12% to 75%. Studies on the influenza virus show that people who supplemented with at least 1,000 IUs of vitamin D a day had fewer and milder flu symptoms. A report, Epidemic Influenza and Vitamin D, in the journal Epidemiology and Infection, noted bone, immune and muscle building benefits of supplementing vitamin D, to achieve blood levels of at least 50 ng/ml. In elderly patients, 4,000 IUs per day were required to attain that level. They suggest some groups, including the elderly, the obese and African Americans may require up to 5,000 IUs per day of vitamin D.” Big pharma and big medicine don’t really want to solve a problem so cheaply.

  • Sad day. STAT has officially joined the ranks of CNN and Fox in their race-baiting and flame-fanning. All for the almighty “story click” that provides advertising revenue…with a potential virtue signaling cherry on top. This site can no longer make the claim it is evidenced based. There is no other explanation that a “senior writer” and her editor would purposefully omit information regarding melanin’s relationship with Vitamin D and the corresponding negative effects on respiratory illness outcomes. This isn’t fringe information. I hope it was worth it Sharon Begley. Did this “story” provide the most clicks you have ever received? Bravo. To achieve this you simply had to disgrace the profession of journalism and play your part in further dividing the human race by planting misinformation. Deplorable. And since this article is lacking in facts let me provide one…purposefully omitting scientific data hurts the cause of unity and anti-racism. Bridges cannot be re-built on a foundation of misleading ideas.

  • The MIT study seems to have been pitched by its authors to suggest that even after controlling for, say, the correlation between African-American race and income, there is STILL a residual disparity in death rates. This seems like a cynical ploy to draw attention to their paper at a time of great race-related unrest. What they actually find is this: “We find a positive, statistically significant, and large correlation between death rates and the share of residents that are African American in the model without state fixed effects, but the correlation is no longer statistically significant when we include fixed state effects.” (pp. 5-6) What their analysis actually suggests is that African Americans tend to live in states that have either done a poorer job of managing the pandemic, or that were simply unlucky in attracting some of the first cases.

    I would add that none of this means that systemic racism is not at play. Racism is undoubtedly responsible for poorer health outcomes overall for African Americans. But the study is designed to isolate race itself from important correlates of race such as income, and thereby determine whether there is a *specifically* racial aspect to the correlation, even after disparities in income and other well-studied correlates are corrected for. As they say, “We control for income in our multiple regression model, so any income disparities between African Americans and other races would be additional to the correlation we uncover.” (pp. 2-3) If their analysis is correct, then there is no such correlation in the case of Covid-19. But if there were, then the first thing a public health analyst should do is to perform the same analysis on yearly deaths due to, say, the seasonal flu. If one were then to find that being African American correlated with worse outcomes for Covid-19 than for seasonal flu, then one would presumably start looking for therapeutically actionable differences, e.g. average vitamin D3 level (as has been suggested elsewhere).

    It’s actually fairly clear that the paper’s strongest finding is that use of public transportation is highly correlated with death from Covid-19. It is this correlation that is of greatest interest from the public health perspective.

  • Feelings of perceived discrimination lead to psychological stress, and studies indicate that stress can significantly influence physiological changes, decreased immunity, and the development of various physical health conditions. Stress however may not affect all individuals who face discrimination. The following article describes how interrelationships among various biopsychosocial variables can be understood:
    Karunamuni, N., et al. (2020). Pathways to Well-being: Untangling the Causal Relationships Among Biopsychosocial Variables. Social Science & Medicine.

    • TLC – that all may be true, but what I see in the papers so far is deaths, not disease rates, but actual deaths, are mostly due to some kind of cytokine storm, and it is not clear to me that is brought on by psychological stress- and, really, is it THAT stressful to be black vs. white? I am not expressing an opinion because I do not know – neither do other white people – or black people.

      Let’s look at why some people get a cytokine storm and some do not. If it is not due to differences in diabetes or obesity, let’s find out what it is and treat it. I am not rejecting any kind of racial disparities in medical care – but there Is NO accepted gold standard for treatment to compare to – in fact, early on in the epidemic, someone who had trouble breathing and got their cousin who works in the bottled gas factory in Calcutta to give them a bottle of oxygen, meant for welding, and just bleed the oxygen out by their nose, might have been better off than someone being intubated on the most expensive respirator, at the best hospital, in New York City
      With no standard of care, it’s hard to say any group was harmed by not getting it.
      There is a paper from some researchers in Italy that has a theory for why black people would be more susceptible to severe disease, do a search if you have the science background, I did not understand it.

    • “Our response to this disease must look beyond the strictly medical.” Perhaps, though attempting to connect a series of dots that relate to stress and inflammation may be less important when dealing with a pandemic than actually focusing on the medical. These comments seem best fit for a discussion over coffee at a Barnes and Noble, when so much about the actual virus is yet to be confirmed. I think we should focus on the immediate medical questions, rather than playing the race card and shifting the dialogue away from a more sure knowledge base to premature policy considerations.

    • Hi Steve: Studies appear to indicate that minority groups can be more stressed than others – below is a reference:

      Williams DR. Race, stress, and mental health: Findings from the Commonwealth Minority Health Survey (2000). Minority Health in America: Findings and Policy Implications from the Commonwealth;. pp. 209–243.

      A minority group can feel socially excluded and therefore possess feelings of not belonging or depravation. I could not locate your reference, but below is an example reference that indicates psychological stress can result in a rise in inflammatory markers including cytokines:

      A.L., Walsh, et al., 2017. The effects of acute psychological stress on circulating and stimulated inflammatory markers: a systematic review and meta-analysis. Brain Behav. Immun. 64, 208–219.

    • Hi DH: Stress and inflammation is important in a pandemic because the body loses its ability to fight diseases when under stress. Stress reduction can go a long way in preventing catching infectious diseases.

  • Is it possible that there is a genetic link such as with sickle cell anemia? In addition, similar studies have shown that the Latino population in the same neighborhoods and poverty levels have not been as susceptible to COVID-19 as the black population has.
    Therefore, we cannot use racism, (even though I am involved in the fight to end it), as a leading reason for this outcome. Fueling the fire does not help us!

    • This seems like an obvious possible contributor that the deep thinkers failed to think deeply about, apparently so invested in painting a need for public policy change that they intentionally avoided a consideration of possible inherent characteristics of race. It seems like an easy line of inquiry (though perhaps expensive or time intensive): find the components of the virus that aid entry and infectivity, or viral and host specific factors that increase the death rate, and then look for any inherited, genetic, or race-related alterations in expression. But, you know, much easier to embrace confirmation bias and call for policy change than develop a viable testing paradigm.

  • As someone who doesn’t live in the US looking in, we see your country as very sick. The level of economic inequality, political polarisation, violence, gun ownership and homicides, inequitable healthcare access, massive per capita carbon footprint etc etc The GDP per capita you have now was built on the backs of people kidnapped from Africa and enslaved for free labour on which to you built your agricultural and industrial economies. There are multiple international indicators that highlight the US’ poor performance compared with other nations, but the idiotic comments in this section stating ‘black people have to help themselves’ show how uncaring and uneducated your sick society is. For those of us watching around the world, our hearts are saddened by the way African Americans are treated in the US; we can only show that we are with you in our BLM protests. I live in New Zealand, a nation with a kind and educated leader.

    • How dare you in another country deem to be so sure about things you know nothing about. If you read ALL the comments you will see a common theme, that being that low levels of Vitamin D are more apparent in black cultures because the darkness of skin inhibits absorption of Vitamin D. Indeed, several studies have emerged from Italy & Spain linking low levels of Vitamin D to Covid-19. In addition the US has taken in more immigrants than any other country in the world. In addition, we have offered opportunity unlike any other nation. Just look at the billionaire atheletes, comedians, TV and movie personalities, Oprah Winfrey, the list goes on and on.

    • Ipngleo, I do dare; there are multiple internationally recognised indicators of the US’ problems with health, education, economic inequality, imprisonment, etc etc So yes, I, and many others looking at your sad declining country do know about these topics and can be sure about these things. I do not discount that vitamin D has a role, but if you look at the Population Attributable Fraction you’ll see that molecular explanations are far far outweighed by differences in the social determinants of health. Billionaire athletes/actors? The sane world doesn’t care about these extreme 0.0001% of the population outlier examples. The distribution of wealth in a society is a far stronger predictor of longevity, infant survival, mental health, wellbeing of women, low imprisonment etc etc than GDP per capita, overall wealth, or these modern-day-aristocrat outliers you gave. Anyway, all the evidence is available, not going to reply to any further posts from you. Am just so thankful I wasn’t born in the US, and extra thankful I’m not a person of colour living there. It’s absolutely disgusting how the US has treated African American people in the past, and how you treat people of colour today. It’s the biggest bully, arms trader, and carbon emitter on the planet, and the sooner it implodes on itself like the Twin Towers the better the rest of the planet will be for it.

    • Bob Roberts – I am not trying to defend slavery – or claim that black people were treated fairly after slavery – but this idea that the wealth of America was created by black people being exploited is nonsensical on it’s face – maybe slavery made some plantation owners and sharecropper people a lot of money -but the wealth of America is based on production, people making things and getting paid reasonably well for it – not exploitation. As a more purely capitalist system than most of the world, the US is definitely more “sink or swim” than most countries – but this idea the wealth came from black people – or them and some other groups – doing all the work for terrible wages is nonsense.
      I can go through many examples, but generally, the Yankees – meaning those in the North of the US – were famous merchants and factory owners well before the US Civil War – the North was almost all white then – the big black migrations to the North came after World War 1, after the US had become a world power, based on the wealth created in the North and Midwest.
      it is important to understand this – not for you so much, but because of anger some black people have, because they believe they are not well off because white people stole from them – that is and extreme form of class resentment and very destructive to society – especially now, as the phenomenon of racial exploitation is absent from the US now, but the teaching that it is going on is rampant.

    • Bob Roberts- Māori and Pasifika people have continuously been suffering from structural racial discrimination, mainly in education, justice and work in (in NZ)–Women’s International League for Peace and Freedom

  • Not true. Sweden, Swizland, Netherlands… have much lower death rate than US. In additionally, the new cases and death cases in US are still not come down significantly comparing to Italy, Spain, France, and Germany.

    • The US, in my view, is doing a very bad job- but Sweden’s death rate is still supposed to be somewhat higher than the US’. I am not 100% sure that is true- better reporting could mean it is slightly less – but with a 5,000 deaths in 10 million population – and the US with 115,000 death in 330 million – Sweden is as much as 30% higher death rate than the US. Really a lot higher, though again, within the possible uncertainty of reporting -but IF it is actually lower it is by a hairsbreadth.

    • I personlly believe continued spread in the US will mean we come up with a very high death toll -but your statement out rates are not coming down while Italy’s, Spain’s, France’s are – yes, because they got to partial herd immunity – I know under the theory of random spread they need more immune people, but it’s clear by now that theory is not well applied to this disease once people become aware of it and take precaution.
      Their rates going down is a sign of huge failures, not success – I personally think the US will most fail in similar ways- just take longer to do it – but in a comparison of what has actually happened, those countries have done pretty badly compared to the US= particularly compared to New York and the areas around New York which were brought down by New York’s severe bungling.

    • Bob: You are glad you do not live in the US. I am also glad that you do not live in the US. we have great difficulty keeping people from illegally entering this country because so many want to come here. It occurs to me that at least a partial answer why blacks do not succed in america is that a great number of them are brainwashed from the time they are 3 years old that they can’t succeed in America because of “white systemic racism”.
      this nefarious and false narrative has been used over and over by the Democratic Party to secure black votes. Those blacks who believe the doctrine is true are unlikely to try if they believe there is no chance for them to succeed. And not trying to succeed guarantees failure. But it does allow them the comfort of blaming their lack of success on “systemic racism” and more specifically on Donald Trump! I again want to express that Bob Roberts and I completely agree that we are both happy that he does not live in the Uited States!

Comments are closed.