Exponential Growth of COVID-19

In the study of epidemiology, the basic reproduction number can be thought of as the number of additional cases we can expect one case in the population to generate. This is usually denoted as R naught or R0.

This number determines how fast a virus spreads. If the R0 is less than one, it doesn’t spread well and dies out pretty quickly.

If it’s two, then one person infects two more people, those two people infect four more, and so on. This is the classic doubling that we see in exponential growth.

According to research from the University of Bern in Bern, Switzerland, the R0 of COVID-19 in Wuhan, China, was believed to be somewhere between 1.4 and 3.8.

We obviously know now that the R0 is nowhere near 1. We are clearly experiencing exponential growth. It’s likely that every person infected with COVID-19 will pass it to about two to three other people.

We know the virus first appeared in late 2019. And we can safely assume that hundreds of, if not more than a thousand, infected people arrived in densely populated cities like New York, San Francisco, and Seattle in early January. From there, the virus spread unhindered for nearly a month.

With an R0 of 3, here is what exponential growth in the spread of COVID-19 would look like:

·  Day 5: 81 new people would be infected.

·  Day 10: Nearly 20,000 more people would be infected.

·  Day 15: Almost 5 million new cases.

·  Day 18: An additional 129 million would be infected.

·  Day 20: Over 1.1 billion new cases.

And here is the problem with determining the spread of COVID-19… Most people have no idea that they have it.

68% of the Population Infected

Strong research out of Iceland determined that around 50% of those who tested positive are asymptomatic. In other words, they have none of the symptoms associated with COVID-19.

Most of the remaining people who have tested positive have only mild or moderate symptoms that do not require hospitalization.

How did Iceland determine these statistics? It did something smart. It tested about 5% of its entire population… whether or not individuals were sick.

And the results are incredibly valuable for understanding COVID-19 and the actual mortality rate.

The World Health Organization did not recognize the situation as a public health emergency until January 30. That means the world was actively, and unknowingly, spreading COVID-19 at an exponential rate up to that point.

New research out of the University of Oxford supports the idea that COVID-19 is already well dispersed among the population.

Its research models determined that COVID-19 has already infected somewhere between 36% and 68% of the U.K. population.

That’s not a typo.

For context, the population of the U.K. is about 67 million. That implies as many as 45 million people in the United Kingdom are already infected with the virus.

It’s also likely that 99% of them don’t know it because they are asymptomatic or have very mild symptoms.

We have every reason to believe that similar infection rates exist in the U.S.

I know that may sound terrifying, but here is where the good news comes in.

The mortality rate of a virus is calculated by determining the number of deaths relative to the total infected population.

The mortality rate for COVID-19 is usually cited as being 2–3%. This rate is based on confirmed cases, not on the total infected population.

These numbers do not account for the number of people who have contracted the virus but have not developed symptoms, or have mild symptoms not requiring medical care and a test.

It means that the actual mortality rate may be far lower… perhaps even lower than 0.1%. Compare that to the mortality rate from influenza in the 2017–2018 season (0.14%).

And research from other countries supports this.

Again, Iceland is unique because it has tested about 5% of its entire population for COVID-19. Only 45 have been hospitalized out of the country’s 1,364 confirmed infections. And there are only four deaths as of this writing.

As the U.S. collects more data on infection rates, the fuller picture of COVID-19 will emerge. And that time is coming quickly.