Between April 25 and May 1, more than 4,600 Indiana residents were tested for viral infections and antibodies for the coronavirus that causes COVID-19 by a team of researchers associated with Indiana University. The participants in the study included more than 3,600 randomly selected people along with 900 volunteers recruited from the African American and Hispanic communities to more accurately represent state demographics.
A news release from the university reports that through random-sample testing the researchers found that during the last week of April, 1.7 percent of participants tested positive for the virus and 1.1 percent tested positive for antibodies. These percentages mean that about 78 participants were currently infected and 51 had developed antibodies against the virus.
Combined figures brought, according to the researchers, the estimated population prevalence of the virus in the state to 2.8 percent, or approximately 186,000 Hoosiers who were actively or previously infected as of May 1. Since 1,067 residents had cumulatively died of the disease by May 1, the researchers calculated the "infection-fatality rate for the novel coronavirus in Indiana to be 0.58 percent, making it nearly six times more deadly than the seasonal flu."
The infection-fatality rate is the percentage of all of the people who become infected by the virus (including those whose cases are asymptomatic or mild and therefore go undetected by medical surveillance) who die of the disease. This is distinct from the case-fatality rate, which reports the percentage of diagnosed cases who die of the disease. The current U.S. case-fatality rate is just shy of 6 percent.
At that time confirmed cases in Indiana numbered about 17,000, which suggests that only about one out of every 11 true infections had been identified through testing symptomatic or high-risk people. The researchers also found that about 45 percent of people who tested positive for active viral infection reported no symptoms at all.
Interestingly, an earlier controversial study by researchers associated with Stanford University and the University of Southern California using only antibody tests sought to estimate how many residents of Santa Clara County (Silicon Valley) California had already been infected by the virus in early April. The researchers conducted a similar study in Los Angeles County. Based on their population screening antibody tests, the researchers estimated that 2.49 to 4.16 percent of the residents of Santa Clara County and 2.8 to 5.6 percent of the residents of Los Angeles County had already been infected in early to mid-April.
Based on these estimates, the California researchers concluded that would mean that by early April between 48,000 and 81,000 people had been infected in Santa Clara County, which is 50 to 85-fold more than the number of confirmed cases at that time. The results of the Los Angeles County study imply that approximately 221,000 to 442,000 adults in the county already had the infection. That estimate is 28 to 55 times higher than confirmed cases at that time in that jurisdiction. Based on these calculations the infection-fatality rates in these studies—somewhere between 0.12 and 0.2 percent in Santa Clara County and between 0.1 percent and 0.3 percent in Los Angeles County—are significantly lower than that reported by the Indiana research team.
In response to the criticisms of their first report, the Santa Clara study researchers re-crunched their data, changing their early April infection prevalence to between 25,000 to 91,000 with a central estimate of 54,000. In other words, the California researchers are still suggesting that undetected coronavirus infections are still 25- to 91-fold greater than confirmed diagnoses. This would concomitantly mean that their infection-fatality rate is also quite low.
Another April study testing some 1,800 randomly selected residents for coronavirus antibodies in Miami-Dade County calculated that about 165,000 residents were infected by the virus. That was more than 16 times the number of confirmed cases at that time. Based on the current Miami-Dade death toll, those results suggested an infection-fatality rate of about 0.2 percent. These results are clearly in line with those reported by the two California studies.
On the other hand, a New York State antibody test study in late April involving 3,000 participants suggests that the rate of mild and symptomless coronavirus infections is only about 10 to elevenfold greater than the number of confirmed cases in those jurisdictions. The New York study calculated that about 2.7 million New Yorkers have been infected, which in turn implies a statewide infection fatality rate (IFR) of around 0.6 percent. These results obviously are more in accord with the findings of the Indiana research team. Assuming the New York blood test data and the Indiana infection and blood test data are reasonably accurate, these studies would suggest that the California studies are overestimating undetected infection rates three to eightfold.
The researchers behind these studies should be applauded for undertaking these complicated studies during the chaos of the unfolding pandemic. So while it is frustrating, it is therefore not surprising that researchers have not yet nailed down just how deadly COVID-19 is. It is, however, sad that the disparate preliminary results of these studies are being selectively used by today's culture war factions to confirm their already existing biases.
Caveat: Other than the Santa Clara study and its update, none of these studies have been published either as preprints or in peer-reviewed journals and so have not been subject to deeper scrutiny by other researchers.