How is COVID-19 like the 1918 flu?
A few folks have asked me how COVID-19 is similar to the 1918 flu. There are two main things I’m considering when I say that.
Mortality rate: The early reports of COVID-19 are showing a mortality rate of 1.5-3%, meaning that 1.5-3% of people who are infected die. This is approximately 10-30 times higher than the mortality associated with seasonal flu in the U.S. and in the same general vicinity as 1918 flu.
But (there is always a but), as with interpreting any science, there are some key things to consider. For one, it’s possible that there are a large number of people with mild, undiagnosed COVID-19 infection. If this is the case, the actual mortality rate is much lower. For another, most of the data are from China where many people smoke and medical care is probably not as strong as in the U.S. Both of these factors could make COVID-19 mortality rates seen to date higher than what we would see here. A final thing to consider is that the mortality rates for both seasonal flu and the 1918 flu are estimates, so our comparisons are not perfect.
Transmission rate: Early reports indicate that each person with COVID-19 infection gives the virus to more than two other people (on average). This is referred to as the transmission rate. There are other factors to consider, but in general the higher the transmission rate the more cases we will see. We think the transmission rate for seasonal flu is less than two but the 1918 flu transmission rate is about the same as what we’re seeing with COVID-19. Again, these are estimates and we don’t yet know if they are correct.
Health departments, in the U.S. and worldwide, are collecting more data every day. We will have better estimates of both of these measures soon. In the meantime, my personal approach is stay calm and be cautious:
Stay home if you’re sick
Make sure our healthcare workers have the supplies they need
Wash your hands and cover your cough
Be kind to those who are impacted by COVID-19
Decrease your exposures where you can