Crudely, generally, and absolutely not universally, deadlier viruses are easier to contain geographically than milder viruses. Ebola, MERS, and SARS all have much higher mortality rates than Covid-19 and were limited to smaller regions. The obvious reason for this is that sicker people are too sick to spread a virus to the community and the world at large. Covid-19 spreads easily because it appears to be spread in the absence of symptoms and for an extended period of time. People who are infected travel, go to work, go shopping, visit hospitals, and so on.

Quite a few people point out that the mortality rate for Covid-19 may be overstated because an unknown number of people probably contract the virus without ever showing symptoms, so these survivors are not a part of official counts. That’s true, but it is also true that people who have died of pneumonia and other infections may also have had undiagnosed Covid-19. No one knows which group of people is larger, so estimating the mortality rate is still just a guess.

Given that the mortality rate is only a guess, experts have made their best guesses at somewhere between 1.0 and 2.7 percent. The mortality rate for seasonal flu is 0.1 percent. Based on this, Covid-19 will cause from 10 to 27 times more deaths than the flu. 646,000 people die from influenza annually. If Covid-19 reaches a similar saturation, that will mean deaths from 6.5 million to 17.5 million people.

Each year, hospitals and surgeries strain under the burden of treating complications related to seasonal flu. Add a few million cases of pneumonia to the mix, and you have the potential for a fairly daunting problem. Panic doesn’t help anyone, but this is a serious global health event.