Welcome to 2020, when people continue to argue about the death rate of a pandemic that’s already killed over 200,000 Americans. It’s been a bit like debating over the size of the flames when your house is on fire and you are wearing a suit made out of dryer lint.
Nevertheless, there’s been a number of reasons why estimating the Covid-19 coronavirus death rate has been challenging. The latest attempt has appeared in a research letter recently published in the Annals of Internal Medicine. It’s a good attempt but take the findings with a Pokemon backpack full of salt.
For the study, a team from the Indiana University Richard M. Fairbanks School of Public Health and the Indiana University School of Medicine (Justin Blackburn, PhD, Constantin T. Yiannoutsos, PhD, Aaron E. Carroll, MD, MS, Paul K. Halverson, DrPH, Nir Menachemi, PhD, MPH) combined two sets of data. The first set was the number of estimated cumulative total of severe acute respiratory syndrome (SARS-CoV2) infections in Indiana as of April 29, 2020. This was based off of a random sample of state residents who were 12 years and older and weren’t currently living in institutions like nursing homes. Based on testing data from April 25 to April 29, 2020, they determined who had active SARS-CoV2 infections (for example, from cotton swab up the nose tests) and who had had infections previously (based on blood tests for antibodies). The resulting estimate was 187,802 cumulative infections in Indiana from the beginning of the pandemic to April 29.
The second set of data was the number of recorded Covid-19 deaths that had occurred in Indiana as of April 29, 2020. This was the number of deaths that had been reported and recorded by that date, amounting to 1099 Covid-19 deaths. Since 54.9% of these were among nursing home residents, the researchers pared the number down to 495.
From these two sets of data, the researchers then calculated the infection fatality rate (IFR) by dividing the number of deaths by the number of infections. Note that this is different from the case fatality rate (CFR), which would be the number of deaths divided by the number of Covid-19 cases, i.e., people who develop symptoms. By definition the CFR should be higher than the IFR.
For the overall non-institutionalized population in Indiana, the IFR came out to be 0.26 percent. In other words, for every 1000 people in the community who had gotten infected, an estimated 2.6 ended up dying. The average age at death was 76.9 years.
The calculated IFR increased with age. It was 0.01 percent for those 12 to 40 years old, 0.12 percent for those 40 to 59 years old, and 1.71 percent for those 60 years and older. Men had a higher IFR than women (0.28 percent versus 0.21 percent).
You may have heard that pandemic has been hitting non-Whites worse than Whites. Well, surprise, surprise, non-Whites had an IFR of over three times that of Whites (0.59 percent versus 0.18 percent). Before you blame age for this difference, consider this result: the average age of death for non-Whites was 73.3 years old compared to 78.9. So non-Whites were dying not only more frequently but also on average at a younger age.
So, what does this all mean? The overall IFR was a little lower than the 0.5 to 1 percent range reported by the World Health Organization (WHO), based on other studies. Undoubtedly, people will begin twisting these numbers like a fishing net made out of Twizzlers to fit their political and business agendas. Therefore, it’s really important to keep in mind what the limitations of this study are and what you can and can’t get from the IFR.
First of all, these results came from a random sample from a single state at a single point in time. You know the saying, what happens in Indiana may stay in Indiana? As is the case with studies, polls, and pizza, samples have their limitations. It may not be the same as seeing the whole pie and could be biased in different directions.
Secondly, it’s not clear how well the estimated number of Covid-19 cases matched the actual number of Covid-19 cases. Testing in the U.S. has been like an alpaca driving a pick-up truck: very haphazard. It hasn’t been clear who is getting tested and who isn’t and what kinds of tests are being used. This was especially true during the first few months of the pandemic
Similarly, the number of reported Covid-19-related deaths is the number of reported Covid-19-related deaths. Reported does not mean actual. Like the number of men who admit that they like Sex on the Beach (the drink and not the act), the number of reported deaths from a disease is typically lower than the actual number. Moreover, the study did not include people who were already sick with Covid-19 during the study time period but passed away after April 29.
Additionally, the study lumped everyone who tested positive for the Covid-19 coronavirus together and did not separate them out by disease severity or even whether they had symptoms. There may be big differences between being exposed to a relatively small amount of the virus and being exposed to a large amount of the virus. Moreover, who knows how the transmission of the virus and the death rate could be changing over time.
Most importantly the results from this study simply give you an idea of the overall population death rate. Population rates are not the same as individual risk. You can’t really use them to predict your chances of death if you get Covid-19.
Ultimately, the IFR is only one measure of the danger of the Covid-19 coronavirus pandemic but certainly not the only measure. Death is not the only problem that an infection can cause. Can you imagine if you relied solely on death as the measure of how you are doing in life? A doctor would then walk in to see you and say, “OK, you look alive. We’re done here.” Even if you survive the initial infection, the virus can cause lots of problems like major respiratory issues or organ damage that could persist well beyond the initial infection. Even if the IFR ends up being one percent or below, that wouldn’t mean that 99 percent of the Covid-19 coronavirus cases are “totally harmless.”