On July 7, I posted five reasons as to why CFR may be decreasing while cases are increasing. One of which was lag time.
In other words, deaths today aren’t indicative of spread today, but rather a reflection of case severity 20-30 days ago. It’s been 27ish days since exponential growth started across several states. We should start seeing an uptick in CFR if this hypothesis is correct.
And we are. This is obvious in TX and CA. Doesn’t look like there is change in FL, AZ, or GA (yet). Given the spread among the younger population, this lag time may be even more than 30 days.
It’s still too early to see the impact of this recent uptick in TX and CA on cumulative CFR (Figure 2).
So, what’s causing this increase in TX and CA? Either we have reached hospital capacity (which we haven’t). OR COVID19’s reach is so wide it’s starting to reach vulnerable populations. OR we are increasingly testing those that are more sick (indicative of a high test positive rate). It’s likely a combination of the latter two. CFR is a difficult measurement because it’s highly dependent on the number cases we catch. For example, if we are only testing high risk populations (like nursing homes), the CFR will be high. It’s typically missing asymptomatic or mild cases that just never get tested.
Because of this, public health decision makers are starting to use Infection Fatality Rate (IFR). IFR estimates the fatality rate among those infected (detected AND undetected cases).
In the US, the CDC’s best IFR estimate is 0.65%. So, on average, 6.5 people of 1000 infected will die of COVID19. A recent publication pooled global IFR; IFR ranged between 0.53% and 0.82%. IFR is a more direct measure of disease severity, although highly dependent on place.
Understanding the true fatality rate has implications for public health planning. Unfortunately, if you thought the CFR was “low”, you are really not going to worry about 0.65% IFR. Given the reach of COVID19, this is still very much a leading cause of death in the US. The morbidity of COVID19 should still be of great concern too.
Love, your local epidemiologist
Data source: COVID19 tracking project. Graphs by yours truly.
Pooled IRC: https://www.medrxiv.org/conte…/10.1101/2020.05.03.20089854v4
CDC report: https://www.cdc.gov/coronavir…/…/hcp/planning-scenarios.html