I’ve often read that the Covid-19 death rate is much worse than that of the seasonal flu, which is typically given as around 0.1% in the US. According to Live Science, that’s the “case” death rate, meaning the percent of people with the flu who die of the flu. The case death rate for Covid-19 is currently thought to be around 1%, or ten times higher than the oft-cited flu death rate. Problem is, the true flu mortality rate is unknown due to inadequate cause-of-death information on US death certificates. As they say, garbage in, garbage out. To quote:
“Most fatal cases of influenza involve pneumonia. Deaths due to influenza-caused pneumonia may be recorded as influenza or as pneumonia, depending on (among other things) whether the medical professional filling out the death certificate has laboratory confirmation of influenza… influenza is not a cause-of-death classification to be trusted. Barring an especial reason, influenza mortality should never be analyzed as a stand-alone cause, but instead should be combined with pneumonia.” Influenza as a proportion of pneumonia mortality: United States, 1959-2009.
“We conducted a systematic review to summarize published estimates of the case fatality risk of the pandemic influenza H1N1pdm09 virus….We included 77 estimates of the case fatality risk from 50 published studies, about one-third of which were published within the first 9 months of the pandemic. We identified very substantial heterogeneity in published estimates, ranging from less than 1 to more than 10,000 deaths per 100,000 cases or infections.” Case fatality risk of influenza A (H1N1pdm09): a systematic review.
“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. …Only counting deaths where influenza was recorded on a death certificate would be a gross underestimation of influenza’s true impact.” Why doesn’t CDC base its seasonal flu mortality estimates only on death certificates that specifically list influenza?/CDC
Since it’s hard to pin down the actual number of flu cases that end in death, epidemiologists often use population-based death rates instead of case-based death rates. And they combine the death rates for influenza and pneumonia. Using that metric, the US death rate for Influenza/Pneumonia in 2018 (last year available) was about 15.3 per 100,000 people As of today, May 8, 2020, the US population-based death rate for Covid-19 US is around 24 per 100,000. More than the death rate for Influenza/Pneumonia - but not by much. While the Covid-19 population-based mortality rate will continue to rise, I doubt its rate will come close to ten times that of influenza/pneumonia (plus other flu-related conditions).
Note that case-based death rate is still the ideal metric for gauging the virulence of Covid-19. Population-based rates muddy the picture somewhat by combining prevalence and lethality. But for case-based death rates, you also have to know the number of people who have caught an infection - i.e., who count as cases - and, thanks to all the untested and asymptomatic carriers, we just don’t have good numbers on that, either for influenza or Covid-19.
References:
Influenza/Pneumonia Mortality by State/CDC https://www.lung.org/getmedia/98f088b5-3fd7-4c43-a490-ba8f4747bd4d/pi-trend-report.pdf.pdf
Noymer A, Nguyen AM. Influenza as a proportion of pneumonia mortality: United States, 1959-2009. Biodemography Soc Biol. 2013;59(2):178‐190. doi: 10.1080/19485565.2013.833816
Trends in Pneumonia and Influenza: Morbidity and Mortality. American Lung Association, Epidemiology and Statistics Unit, Research and Health Education Division. November 2015. https://www.lung.org/getmedia/98f088b5-3fd7-4c43-a490-ba8f4747bd4d/pi-trend-report.pdf.pdf
Wong JY, Kelly H, Ip DK, Wu JT, Leung GM, Cowling BJ. Case fatality risk of influenza A (H1N1pdm09): a systematic review. Epidemiology. 2013;24(6):830‐841. doi: 10.1097/EDE.0b013e3182a67448