Aren't the vast majority of us going to get infected by the Corona Virus?

[cmosdes]

@Sage_Rat

The R0 is the population-level effect of the virus. It’s how quickly it grows, on average, not how many people are infected by a single person. A large number of people never even get the disease. Only a small percent ever become infectious, and they have to make up for all of the people who are naturally immune, non-infectious, or otherwise never pass the disease on.

An average spread of 2.5 might mean that 10 people never spread it and 1 person spreads it to 28 people.

I would also note that an R0 is a count of people infected, rather than exposed. So we’re not saying that of the 11 people, 1 of them was infected and exposed 28 other people to the virus, they actually gave it to 28 other people.

That’s probably hard to accomplish, so the average infectious person is probably not spreading to quite that many people, but it is still an R0 of 2.5.

Averages can be misleading, to be sure. You talk about “average person” exposing 30 people and being unable to identify 6 of them. In order to have an infected person in the group of 6, the “average person” would have had to infect 5 total people. Twice R0. To keep the averages working out, someone else needs to infect 0 other people. In other words, this can’t continue on indefinitely, where each new infectious person can’t then infect 5 more people, 1 or more who are untraceable. That would make R0 5, not 2.5.

In other words, in a specific case, your numbers are reasonable. As a population average, it doesn’t. When you take the population as a whole, the average needs to be 2.5. Your example of how 1 person can infect 10 others, those 10 others never spread it to anyone else, so that path dies and it doesn’t matter we can’t trace 2 of them.