Typically reported as case fatality rate (CFR) because it’s easy to calculate (# of deaths/# of cases). CFR is around 3% in the US. In other words, 30 people of 1000 infected will die. However, we know that 3% is higher than the “real” death rate because we have mild or asymptomatic COVID19 infections. These people never get tested, and thus not included in CFR.
So, epidemiologists and policy makers use Incidence Fatality Rate (IRF). IFR estimates the death rate among detected AND undetected cases. COVID19 doesn’t make this easy to calculate. We need the “true” COVID19 infection rate in a community (which we don’t really know). So, we have relied IFR’s calculated from cruise ships or from mathematical stimulations.
Until now. A study was published on September 2.
Scientists in Indiana used statewide data and calculated an IFR of 0.26%. So, on average, 2.6 people of 1000 infected in Indiana will die. This number ranges dependent on age and other factors (see Figure). It’s important to note that this IFR excludes kids (less than 12 years old), prisoners, and nursing home cases and deaths.
• CDC’s best IFR estimate is 0.65% for ALL Americans. So, on average, 6.5 people of 1000 infected will die.
• The global COVID19 IFR ranges between 0.52% and 0.82%.
Why is this number so important? It puts the severity of this novel virus into perspective (at least in terms of mortality). The number impacts how we determine our public health response strategies. We are lucky that this number is relatively low. Rabies is 100%, ebola is 50%, smallpox is 30%, polio is 15%, chicken pox is 0.8%. The problem is that COVID19 is a sneaky little thing; it spreads way too easily without us knowing (unlike the more lethal diseases). This has resulted in a far COVID19 reach and, thus, 188,000 deaths in the US.
P.S. Before you ask, the highly cited flu IFR estimate is 0.1%. This number is calculated from hospitalizations. It excludes asymptomatic people or people who never get tested (which is about 65%-85% of flu cases). So, 0.1% is typically considered high for the flu. Nonetheless, if we take these imperfect numbers, COVID19 is between 2.6-6.5 times more lethal than the flu.
Data Sources: Indiana Study: https://www.acpjournals.org/doi/10.7326/M20-5352Global IFR: https://www.medrxiv.org/conte…/10.1101/2020.05.03.20089854v4CDC IFR: https://www.cdc.gov/coronavir…/…/hcp/planning-scenarios.htmlFlu IFR: https://www.cdc.gov/flu/about/burden/how-cdc-estimates.htm