Why does it seem like COVID-19 infections go up so quickly?

Infection and Spread Staying Safe

A: TL; DR Exponential math (think curved line like a J shape graph).

Let’s assume that each person infected will infect two other people (in other words, the number of people infected doubles every two weeks). If we start with one case on Week 1 and each individual passes the virus to two other people, at Week, 52, we would have had over one hundred million cumulative cases. Yes, you read that correctly.

On the other hand, if we assume that each person infected will infect one other person (like with linear math, think straight line graph) and that the virus grows in a linear fashion, it doesn’t seem so bad. If we start with one case on Week 1 and each individual passes the virus to one other person (if we go up by two weeks, one more person will get an infection), at Week 52, we would have had 26 cumulative cases.

Exponential Growth of New Cases if Doubling the Number of Infections Per 2 Weeks:

Week 0: 1
Week 2: 2
Week 4: 4
Week 6: 8
Week 8: 16
Week 10: 32
Week 12: 64
Week 14: 128
Week 16: 256
Week 18: 512
Week 20: 1,024
Week 22: 2,048
Week 24: 4,096
Week 26: 8,192
Week 28: 16,384
Week 30: 32,768
Week 32: 65,536
Week 34: 131,072
Week 36: 262,144
Week 38: 524,288
Week 40: 1,048,576
Week 42: 2,097,152
Week 44: 4,194,304
Week 46: 8,388,608
Week 48: 16,777,216
Week 50: 33,554,432
Week 52: 67,108,864

This is a big difference and part of why we don’t always perceive the threat when cases are low. They start to grow slowly until they reach very high numbers. At that point, growth will continue to increase at an alarming rate. This is where we are right now in many parts of the United States.

The good news? In reality there are some subtleties. Non pharmaceutical interventions matter. Think physical distancing, moving outdoors, wearing a mask, restricting contacts and time spent with them, and basic hygiene measures. We also know that some people do spread more than others, although we aren’t quite sure yet why that is. See our previous piece on super spreading for a bit more detail (https://bit.ly/2IXFXm0).

And in simple terms, if we had just 1 case of COVID-19 on January 1 and no control measures were put into place, we would have over 100,000,000 cases by the end of 2020 (nearly 1/3 of all Americans). Of course, there are some nuances to this message. Sometimes people spread a lot (think superspreader events where one person spreads to 50 or more people) and sometimes people spread not at all (because they did not get the virus or they simply don’t transmit it).

The good news? The actions you take do make a difference. You can be the one Pom Pom that stays out of this. And you can share this message with others.

Stay safe. Stay sane.

With Love,
Those Nerdy Girls

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