March 19, 2020

POSSIBLE EXCELLENT NEWS ON COVID-19: This morning, a friend forwarded an abstract of a study from the Center for Evidence-Based Medicine estimating that the CFR (case fatality rate–the number of reported deaths per number of reported cases) is only .1%, i.e., one out of a thousand. I was going to pass it on earlier, but I really couldn’t make heads or tails of how they came up with that figure, so I emailed them, and they updated their post with this:

How do we arrive at this CFR figure?

The current COVID outbreak seems to be following previous pandemics in that initial CFRs start high and then trend downward. In Wuhan, for instance, the CFR has gone down from 17% in the initial phase to near 1% in the late stage. Current testing strategies are also not capturing everybody: at least 50% on Diamond Princess were asymptomatic who usually wouldn’t get a test; in South Korea, considerable numbers who tested positive were also asymptomatics. Asymptomatic people and mild cases are likely driving the rapid worldwide spread. Early CFR rates are subject to selection bias as more severe cases are tested – generally those in the hospital settings or those with more severe symptoms. Mortality in children seems to be near zero (unlike flu) which will drive down the CFR significantly. In Swine flu, the CFR was fivefold less than the lowest estimate in the 1st ten weeks (0.1%)

Therefore, to estimate the CFR, we used the lowest estimate, currently Germany’s 0.25%, and halved this based on the assumption that half the cases go undetected by testing and none of this group dies. Our assumptions, however, do not account for some exceptional cases, as in Italy, where the population is older, smoking rates are higher and antibiotic resistance is the highest in Europe, which all can act to increase the CFR. It is also not clear if the presence of other circulating influenza illnesses acts to increase the CFR and whether certain populations (e.g., those with heart conditions) are more at increased risk.

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