One way we can compare the two outbreaks is by looking at case fatality rates: the share of infections that lead to death. This is always difficult to estimate because there are likely more infections than have been identified by medical authorities. According to
Johns Hopkins researchers, as of this writing there have been 111,363 cases of Covid-19 and 3,892 deaths, for a case fatality rate of about 3.5 percent.
But you should
take that number with a grain of salt. Countries’ testing protocols vary widely and many,
including the US, have only tested a few thousand people while others, like
South Korea, have tested hundreds of thousands. That means the denominator for the case fatality rate — the total number of infections — is uncertain, and might be undercounted due to lack of testing. In South Korea, the case fatality rate is
currently 0.7 percent, suggesting that better testing might yield more accurate, lower rates. At the same time, as
Julia Belluz explains, accurately measured fatality rates are also going to vary significantly from country to country due to differences in health system capacity, low- and middle-income people’s access to health care, etc.
The case fatality rate of the Spanish flu is often cited as 2.5 percent, but this is likely a dramatic underestimate, as science writer
Ferris Jabr has written.
The most frequently cited death statistics for the Spanish flu come from
Niall Johnson and Juergen Mueller’s 2002 study, which estimated the death toll at 50 million and warned that this might be as much as a 100 percent underestimate, implying a total toll of 100 million. A more recent
2018 paper by Pete Spreeuwenberg, Madelon Kroneman, and John Paget gets a much lower estimate of 17.4 million. If the frequently cited estimate of 500 million infections globally is correct, then the latter death toll implies a case fatality rate of 3.5 percent, but using a higher death toll of 50 million, the fatality rate rises to 10 percent.