All Else Is Not Equal: Racial Disparities in US Covid Casualties

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 (1.18 = 2.1), whereas blacks would be 7 years older than whites (1.17 = 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.

 

Covid Undercounting in Africa?

It would seem that Africa has been spared the worst of the pandemic, with most countries on the continent reporting much lower case counts and fatalities than Europe and the Americas. Why? Maybe it’s the climate — the virus seems to spread fastest in cold dry conditions. Or maybe the continent’s relative isolation has buffered it from travelers carrying the virus with them from harder-hit areas of the world.

Now a couple of studies suggest that the situation in Africa is worse than the numbers would indicate.

The other day a friend sent me the draft of an article summarizing a seroprevalence survey, conducted in Addis Ababa Ethiopia in late April, that found 8% covid prevalence. The official count as of late April showed only 125 test-positives cumulative and 1 covid death in the whole country, which has a population of 112 million. Could the antibody tests the researchers used have been grossly inaccurate? Not according to the validation data reported in the abstract. There certainly were places in the world that had prevalence levels of 8% or higher in late April, and Addis Ababa’s crowded conditions could certainly have accelerated contagion. So it’s not out of the question that the findings reported in the abstract accurately reflect the situation on the ground at the time.

A few days later I came across another study, published in the 1 January online issue of Science. This Kenya study is based on analysis of more than 3,000 blood donor samples collected between 30 April and 16 June 2020. They found a seroprevalence of 5.6% — comparable to the Ethiopian seroprevalence survey. The much lower official tallies for Kenya as of mid-June are very similar to those of Ethiopia. This Kenyan study also found higher seroprevalence in the big cities, again comparable to the Addis Ababa study.

The Kenya study authors point out that covid mortality is much lower than might be expected for that level of infection because covid is fatal mostly for older people, and older people comprise a much smaller percentage in Kenya than is the case in the US and Europe. In my most recent post I updated my age-adjustment algorithm to take into account countries with very young populations. For Ethiopia and Kenya, both with median population age of 20 years, the age-adjusted covid fatality rate is 0.06 percent — a fraction of the US’s 0.65 percent and lower than the influenza fatality rate. 

It’s certainly possible that in the early days of the pandemic nobody in these countries was recognizing covid infections. The official counts in both countries started climbing in late June — maybe that jump is attributable not to a spike in contagion but to the onset of more accurate diagnosis and reporting. Alternatively, the official case and death counts from Ethiopia and Kenya might continue to be grossly underreported, in which case the infection rates for those countries might be among the highest in the world rather than among the lowest.

For comparison’s sake, the IHME’s estimated infection rates for Ethiopia and Kenya are very close to my own, suggesting a comparable age-adjustment factor. However, they rely on the official death tallies in estimating the cumulative infection percentage, which might represent a significant undercount.

So it’s a matter of gradually closing in on better estimates and reducing the uncertainties, to which both of these seroprevalence studies contribute significant information. Hopefully vaccination will start drastically reducing the counts everywhere.