Why are we so worried about a virus that’s ‘only’ killed 21,000 people worldwide?
Please note this post was written on March 21, and these numbers are changing daily. The graphs presented below are to illustrate exponential growth of a virus pandemic, and do not account for population densities, control measures, or decreased transmission as the number of infected individuals increases over time. The number in the title is current as of March 25th.
At present, most of us do not know anyone who has tested positive for SARS-CoV2, and even fewer know anyone who has died. So why are governments going to extreme measures to stop a virus that currently doesn’t seem to pose an immediate threat to most people? The answer is exponential growth. When viruses infect a naive population (as with SARS-CoV2), they can spread exponentially. But what does this mean? Exponential growth occurs when the size of a population increases by a set factor greater than one over a given period of time. In other words, a population is doubling at a regular interval. For illustration purposes, we can use SARS-CoV2.
Right now, the number of confirmed cases of SARS-CoV2 is doubling approximately every 4 days. This means that globally the number of confirmed cases outside of China will increase from 299,125 to 598,250 in the next four days. In a little over a week, we will have over 1 million cases globally. In less than a month, we could have 38,288,000 cases globally. This exponential growth is illustrated below - within a matter of months, SARS-CoV2 could spread to infect ½ the world population.
Data extrapolated by Rachel Temple based on numbers provided by Johns Hopkins University
While the spread of the virus will eventually slow once a significant number of individuals have been infected, what is more concerning is the number of people that might require hospitalization. Right now, 10 - 20% of confirmed cases require hospitalization. Unless we slow down the spread of this virus, if we assume a 10% hospitalization rate, we could be looking at over 300 million people requiring hospitalization by May 15.
Data extrapolated by Rachel Temple based on numbers provided by Johns Hopkins University
This number - 300 million people requiring hospitalization globally in a little over 2 months is what has many governments going to extreme measures to contain SARS-CoV2. Especially when this number is compared to the number of ICU beds we have available (depicted by the red line in the figure below).
March 16, 2020 paper published by the Imperial College COVID-19 Response Team
The current case-fatality rate for COVID-19 is over 4% of confirmed cases. Even if we assume a more modest case-fatality rate of 1% to account for unconfirmed cases, or even 0.1% - the same as seasonal flu, the number of deaths globally would be in the millions.
Data extrapolated by Rachel Temple based on numbers provided by Johns Hopkins University
To put this in perspective, every year flu kills 250,000 - 500,000 people, which is 10 - 100 times less people than SARS-CoV2 could kill. If allowed to spread unabated in the USA and UK, The Imperial College COVID-19 Response Team projected that COVID-19 could kill over 2 million individuals in the USA and over 500,000 in the UK by August.
March 16, 2020 paper published by the Imperial College COVID-19 Response Team
Even if we reduce the percentage of the population infected to only 20% using public health measures like social distancing, scientists still estimate as many as 2 million Americans could die (see below).
March 23, 2020 paper entitled: Fair Allocation of Scarce Medical Resources in the Time of Covid-19
Fortunately, there are ways we can change the trajectory of this pandemic. Within 6 days of China shutting down Wuhan city (date marked with red star), the number of actual cases in China started to drop, though there was a longer delay (~2 weeks) until diagnosed cases in Wuhan started to drop off (this is due to the incubation time of the virus and new diagnosis measures put into practice Feb 5). Now, China is consistently reporting less than 10 new cases a day.
Modified from a Feb 24, 2020 paper entitled: Characteristics of and Important Lessons From the Coronavirus Disease 2019 (COVID-19) Outbreak in China, JAMA
Right now, the best option we have to slow down the spread of SARS-CoV2 and flatten the curve is extreme social distancing. We should avoid any unnecessary interaction with people outside of our immediate household. Leave your house only when necessary. If you are sick, stay isolated in your home and do not leave. This worked for China. From the beginning of the pandemic, South Korea successfully implemented widescreen testing, as well as isolation and contact tracing of any infected individual rather than countrywide lockdowns to control virus spread. A similar model could be adopted by other countries after the lockdowns are lifted to prevent a resurgence of the pandemic.
Finally, wash your hands and do not touch your face. This will eventually end, but we will need the help of every person to get through this as quickly and with as little loss of life as possible.
For a more detailed explanation of exponential growth and pandemics, please watch the video below.
If you are interested in tracking the total number of COVID19 cases, deaths, and recoveries around the world, this website updates hourly. As always, wash your hands and do your part to flatten the curve.
Rachel Temple, PhD
Rachel received her PhD in virology from Pennsylvania State University. She then went on to a post doctorate in Dr. Joshua Obar’s lab at Dartmouth College. In Dr. Obar’s lab, Rachel studied the immune response to influenza virus infection and how comorbidities such as asthma, can increase the severity of disease. Now Rachel works with STEMCELL TECHNOLOGIES in the Philadelphia area.