Friday, July 31The most common measure for the dangers associated with a virus is its infection fatality risk. Because we have a difficult time estimating how many people are infected, infection fatality risk has been somewhat elusive. Places in Europe estimated it at over 1 percent, and an early study from Stanford estimated it at 0.26 percent. The general number assigned to seasonal influenza is 0.1 percent, so how we think about risk relative to flu is a real issue.Before we get to that, remember we did talk about R0 a few blogs ago, and how R0 is higher for COVID-19 than it is for the flu. So, before we assign all the death danger to the infection fatality risk, remember that two to five times more people will catch COVID-19 under the same circumstances as would catch the flu, so whatever number of fatalities we come up with, it needs to be scaled up because COVID-19 is much more contagious and will infect more people. I also do not want to discount enduring health impairments associated with COVID-19, as those appear to be a reality for cases that make it to inpatient status.In New York City, around the end of April, they estimated that 21% of all residents had become infected with COVID-19. Roughly 23,000 people from New York City died of COVID-19, and that is 0.27 percent of the population. When we do the math, we come up with an infection fatality risk of 1.29 percent. Estimates from professional epidemiologists in other populations were all over the map, from 0.58 percent in Indiana to that estimate in New York City.really salient point, however, is that older people have a pronounced tendency to have a worse course of illness with COVID-19 than younger people. As scientists lock onto this point, they began to converge in their estimates of infection fatality risk, or IFR.This pre-print has a really nice figure in a meta-analysis of studies estimating the total number of infections using antibody sampling, and mortality risk. They conclude that the infection fatality risk differences in different contexts comes down to the age of those infected. Older people die at much higher rates than younger people, and the summary graph is shown below:This study agrees with nearly everything I have seen on infection fatality risk, and applied to the U.S. population generates estimates of infection fatality risk of around 0.65 percent, which is the number the CDC typically uses. The new drugs being used for COVID-19, mainly remdesivir and dexamethasone, seem to be cutting this death rate even more, closer to 0.5 percent, and we can look forward to further treatments in the fall cutting this rate even more.But for now, we are at 0.5 percent, which is at least five times deadlier than flu, and two to five times more contagious. COVID-19 has mortality risks that are 10-25 times higher than a typical seasonal influenza. Contact Dave Blake.