How many people in the US have contracted covid since the beginning of the outbreak? Case counts of diagnostic test-positives underestimate the number of infections because a sizable percentage of people who’ve been infected never get tested. Death counts are a more accurate lagging indicator of infections, because deaths are relatively more accurately recorded and because a relatively stable percentage of people who get infected eventually die from the disease. According to my quick-and-dirty algorithm, the total number of covid infections equals the total number of covid deaths divided by .0065. As of 18 February 2021 there have been 505K covid deaths in the US, which translate into 77.7 million covid infections. The population of the US is 329 million, so around 24 percent of Americans have been infected with covid.

All else equal, older people who get infected are more likely to die from covid than are infected younger people; consequently, the divisor in the deaths-to-infections algorithm is age-adjusted. The median age of the US population is 38 years. For populations with a higher median age than the US, the .0065 divisor is increased by 1.1 to the Dth power, where D = the difference in median age from 38. For populations with a lower median age than the US, the divisor is decreased by 1.1 to the Dth power.

According to the CDC, Hispanic Americans are 2.3 times as likely to die of covid as are white Americans, while blacks are 1.9 times as likely as whites. All else equal, it would be expected that this racial discrepancy in fatalities could be explained by median age differences. Adjusting upward from the .0065 covid fatality rate, the median age for Hispanics would project to be about 8 years older than whites (1.1^{8} = 2.1), whereas blacks would be 7 years older than whites (1.1^{7} = 1.9). In fact, however, the median age for white Americans is 44 years, whereas for Hispanics it’s 30 years — 14 years *younger* than whites — and for blacks it’s 35 years — 9 years *younger* than whites. All else equal then, the algorithm would project a Hispanic covid fatality rate of 1.1^{-14} = 3.8 times *less* than whites; for blacks, a covid fatality rate of 1.1^{-9} = 2.4 times *less* than whites. So, taking into account the relatively young age of these minority groups, their high covid fatality rates for US minorities are even more glaring than the raw numbers indicate.

To calculate the relative risk of covid infections for Hispanic and black Americans relative to white Americans, multiply their observed relative risk of their having died of covid by their age-adjusted relative expectation of covid mortality based on the algorithm:

- Hispanic = 2.3 x 3.8 = 8.7 times as likely as whites to have been covid-infected
- Black = 1.9 x 2.4 = 4.6 times as likely as whites to have been covid-infected

The US population is roughly 60 percent white, 19 percent Hispanic, 12 percent black, 9 percent mixed or other. For simplicity’s sake, I’ll eliminate the mixed/other category, rounding the numbers to 66% white, 21% Hispanic, and 13% black. Of the total number of Americans who’ve been infected by covid, the racial proportions are estimated as:

White (.66 x 1) + Hispanic (.21 x 8.7) + Black (.13 x 4.6) = 0.66 + 1.83 + 0.60 = 3.09

- White = .66/3.09 = 21% of US covid infections.
- Hispanic = 1.83/3.09 = 59% of US covid infections.
- Black = .60/3.09 = 19% of US covid infections.

If these estimates are roughly accurate, then of every five Americans who have been covid-infected to date, one is white, one is black, and three are Hispanic.

Overall, 24 percent of Americans have been infected by the covid-19 virus since the beginning of the outbreak. What proportion of the members of each of the big three racial groups have been infected?

- White = 21% of the 24% infected, divided by 66% of the population = 8% have been infected.
- Hispanic = 59% of the 24% infected, divided by 21% of the population = 67% have been infected.
- Black = 19% of the 24% infected, divided by 12% of the population = 38% have been infected.

Again if the estimates are roughly accurate, then Hispanics are approaching the threshold for herd immunity in the US, even before widespread vaccination.

The estimated racial disparities in covid infection rates are likely overstated. All else equal, a 38-year-old infected with the coronavirus has a 0.65% chance of dying from the infection, irrespective of race. But all else isn’t equal. American Hispanics and blacks in America tend to have more comorbid conditions for their age than do their white counterparts, so a relatively higher proportion of their infections prove fatal. Which is a more dire indicator of racial disparity: a higher infection rate, or a higher fatality rate? In the US, Hispanics and blacks suffer massively from both.

Based on data through 2014 compiled by the CDC, here are life expectancies in the US by race:

– White = 79.1 years

– Hispanic = 82.9 years

– Black = 75.5 years

Age is associated with increased comorbidities and with death from all causes, including viral infections like influenza. The life expectancy deficit for African Americans could account for some of their increased covid death rate. On the other hand, Hispanic Americans live longer than white Americans, suggesting strongly that their enormously increased vulnerability to covid isn’t attributable to underlying frailty and illness.

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From this 17 February article exploring possible explanations for the sudden precipitous drop in US covid case counts:

If, per analyses in this post, Hispanics account for 60% of the US cases, and if two-thirds of HIspanic Americans have already been infected, and if Hispanics are socially isolated from non-Hispanics in this country, then the virus’s path forward in the US may have been narrowed by means of racial segregation.

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Covid-19 and Obesitya March 2021 report from the World Obesity Federation, cites a number of studies indicating that obesity substantially increases the odds of covid infection, severity, and death. I’ll look at this report in more detail as a comment to this earlier post on international infection rates; here the question is whether differences in obesity rates could account for demographic differences in infection rates in the US.According to the CDC, the US obesity prevalences among adults are:

– white non-HIspanic = 42%,

– black non-HIspanic = 50%,

– Hispanic = 45%.

These differences likely account for a relatively small proportion of the large observed differences in age-adjusted fatality rates among US ethnic groups. The obesity rates for each of these three ethnicities would place them in the highest obesity category on an international scale — three times as high as most countries in Africa and Asia.

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From this 10 March Reuters article:

“While U.S. communities of color are at higher risk for severe or fatal COVID-19 infections, white people have been vaccinated at twice the rate of Blacks and two-and-a-half times the rate of Hispanics, according to a March 1 study by the Kaiser Family Foundation.”

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