Covid vs Flu: Comparing All Cause Mortality Year Over Year
When will Covid-19 become Flu-like in its mortality impact?
Early on in the pandemic, referring to Covid-19 as “the flu” or "similar to the flu” invoked controversy. Those who compared to flu were accused of downplaying the impact of the virus. Many were just trying to get a baseline for what we might expect the overall impact on the population would be. While some might have been trying to minimize, others were merely asking a fair question: how bad will it be?
Anthony Fauci wrote in the New England Journal of Medicine1 on March 26, 2020:
…the overall clinical consequences of Covid-19 may ultimately be more akin to those of a severe seasonal influenza (which has a case fatality rate of approximately 0.1%) or a pandemic influenza (similar to those in 1957 and 1968) rather than a disease similar to SARS or MERS, which have had case fatality rates of 9 to 10% and 36%, respectively.
So the flu comparison is apparently not a right-wing motivated attack on science after all. Ironically, the statement by Fauci set the stage for an error of historical proportions2, because it inaccurately conflated the infection fatality rate of seasonal flu, with the case fatality rate. The difference between those two rates has been the subject of confusion among the general public and it continues still. Using only those who were tested for a virus as the numerator, as opposed to an estimate based on population seroprevalence (the number in the general population who have antibodies), will always over-estimate the true fatality rate.
As important of a distinction as that is, and as critical as ascertaining the true infection fatality rate3 is- the expected burden of mortality of Covid-19 upon the overall population is the central issue. If IFR is low, and few infected, than overall burden is low. If IFR is low, yet almost everyone gets infected, then it will have a bigger impact on the population.
When we compare historical mortality from Influenza with current mortality from/with Covid-19, it’s important to caveat that we are actually counting differently. The CDC explains how they estimate the burden of seasonal influenza4.
Seasonal influenza may lead to death from other causes, such as pneumonia, congestive heart failure, or chronic obstructive pulmonary disease. It has been recognized for many years that influenza is underreported on death certificates. There may be several reasons for underreporting, including that patients aren’t always tested for seasonal influenza virus infection, particularly older adults who are at greatest risk of seasonal influenza complications and death. Even if a patient is tested for influenza, influenza virus infection may not be identified because the influenza virus is only detectable for a limited number of days after infection and many people don’t seek medical care in this interval.
Notice that the way the don’t account for Flu deaths: PCR testing. A different standard of accounting for Covid-19 deaths has been applied than was used for Flu. While there seems to be some real examples over-counting deaths in some instances, there have been studies that have asserted under-counting5 as well.
A simple way to look at this issue is to observe overall mortality year over year in years previous to 2020 and 2021, comparing the impact flu typically has on mortality with the impact of Covid-19. Using data from CDC’s Provisional Counts of Death by Select Causes,6 we can see the overall shape of the topline weekly mortality, and “underneath” that topline, the impact that Flu and Covid have had.
In the below gif you can see that in years 2016-2019, Flu has a noticeable impact in the winter season. We know that flu surges in the winter and that shows up clearly in all cause mortality. Knowing that Flu deaths might be undercounted is important to keep in mind here, as winter is respiratory virus season and the pattern of increased mortality in winters is a well established pattern.
For years 2020 and 2021, the impact of Covid is obvious, and the topline shape of mortality is essentially an imprint of the Covid mortality that you can see underneath.
As the most recent wave peaks and subsides, I believe a fair question is when will Covid-19 become Flu-like in its mortality impact? Are we there yet?
Comparing 2019, 2020, and 2021 in the chart below, we can see that 2021’s numbers are still being filled in, and I will update the chart as counts become finalized over the coming months.
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