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What's the Big Deal?

Last Updated: 14th May 2020

How infectious is COVID-19?

Whether or not a disease is infectious makes a big difference on how it is categorised and managed. In the early days of the COVID-19 outbreak, a number of graphs went viral showing how many global deaths occurred annually from other health conditions and then compared those to the small number of deaths from COVID-19. It attempted to make the point that we shouldn't react so much to COVID-19 when we don't react so much to all these other situations that have higher deaths. However, all the diseases listed were not infectious. This is important because the number of expected deaths we expect to have from non-infectious diseases like Cancer, MS or Alzheimers, are not likely to double over the next year. However, without any control measures in place, COVID-19 deaths don't just double over a year - they double every 2-4 days.


Infectious diseases need to be thought of in exponential terms. Unfortunately, this is not how we are used to thinking. There's a famous story of a man who tricked an emperor using a simple grain of rice and a chessboard. The emperor was so impressed with the man he said, 'ask anything you want except for my kingdom and I will give it to you as thanks'. The man took a single grain of rice and placed it on a chessboard. 'I  am a simple man, all I ask is for you to give me one grain of rice for the first square, two for the second square, four for the third, eight for the fourth, and to keep doubling the rice for the 64 squares on this board'. The emperor smiled warmly, surprised the man had asked for so little. He solemnly promised it would be so and instructed his treasurer to make the arrangements. Yet when the emperors treasurer calculated the rice that would be needed, it turned out to be more rice than the entire kingdom could produce in a century. To keep his word, the emperor asked if the man would accept his kingdom instead.

The man was able to trick the emperor because our minds are used to thinking in linear not exponential terms. It's remarkable to think that on that 64th square alone, the emperor needed as much rice as all the previous 63 squares combined. In fact, it would have taken the first 55 squares for the man to accumulate just half of 1% of the total rice he was owed at the end. The last few squares were the difference between the emperor losing a years worth of rice or losing his entire kingdom.

These dynamics apply to all infectious diseases. To measure this, epidemiologists use something called a diseases 'Basic Reproduction Number' or 'R0' (pronounced R-Naught). This describes how many people someone is likely to infect. An R0 of 1, means that every person who has the disease is likely to infect 1 other person. Any R0 lower than 1 means the disease cannot sustain itself and will die out. This is like if rice man asked the emperor to halve the grain of rice every square instead of double it. Instead of the rice pile growing larger and larger, it would grow smaller and smaller. An R0 higher than 1 has the possibility of becoming an epidemic.

This is part of the reason why it's hard to get rid of viruses like the Common Cold (eg. Rhinovirus) which has an R0 of 1.2 - 1.83. Or the Flu - which varies season to season but generally averages an R0 of 1.68. Previous viruses from the Coronavirus family have ranged from an R0 of 2.7, to as high as 8. We don't yet know the R0 for COVID-19, but it's thought to sit around 2.6-2.79 [1] [2] [3]. This is much better than an R0 of 8, but in exponential terms, it's still drastically higher than something like the Flu. After just 64 cycles COVID-19 would have infected 888 billion times the number the Flu could infect with an R0 of 1.68.


As governments implement different measures to slow the spread of COVID-19, they are essentially fighting against the diseases R0. The higher the R0 the harder this is to do. The measure of how successfully they are doing this is expressed by epidemiologists in another number called the 'Effective Reproduction Rate', or 'R-eff''. This number looks at how fast the disease is increasing or decreasing separate from whatever it's natural R0 is. This means that even if a disease has an R0 as high as 10, if daily cases are remaining stable, neither increasing or decreasing, then the Effective Reproduction Rate is 1. If that number can be brought below 1, the disease will be unable to sustain itself over time.

Because COVID-19 is so infectious, it only takes a few cases to create a high growth rate. One paper suggested that all it took for COVID-19 to become self-sustaining in a city was for there to be as few as 4 unconnected cases. This is a challenging finding for governments who are keen to minimise lockdowns as much as possible.

Managing R-eff

How easily the Effective Reproduction Rate can be controlled is hugely dependant on each disease, the resources a country has, and how early in the outbreak interventions are implemented. Controlling the Effective Reproduction Rate relies on doing a few key principles well:

  • The ability to tell when someone is infected,
  • The ability to monitor where in a population the disease is,
  • Knowing how to to effectively quarantine people with the disease to stop its spread,
  • The ability to identify and quarantine primary and secondary contacts an infected person comes in contact with to stop those contacts from spreading the disease further.

The better a country is able to do these four things, the more social mobility and economic activity they can afford. Countries without the ability to control these dynamics, will find themselves torn between increased economic hardship and increased inability to control the spread.

Whilst governments have shown they can bring the Effective Reproduction Rate of COVID-19 below 1, many have used unsophisticated and costly ways of doing this such as lockdowns. Without any known treatment, and the possibility of a vaccine still at least a year away, governments will need to either eradicate the disease or find less costly ways of controlling the Effective Reproduction Rate. Their ability to do this will directly correlate to stronger health and economic outcomes.

What causes complexity, is that currently both sophisticated and unsophisticated methods of controlling the Effective Reproduction Rate grate against a number of core national values in many cultures. These include a sense of autonomy and freedom. Habits around social connectedness and expression of community. Feelings toward rights to privacy. And expectations around citizenship. This is further compounded in communities experiencing reduced or lost trust in institutions.

In countries where certain values are high, and institutional trust is low, health and economic interventions become increasingly wrapped in existing underlying sociological tensions. To navigate this, governments will not just have to consider what the best technical options are, but also understand what their populations are willing to accept and champion.

Is it a big deal?

When it comes to measuring how infectious a disease is, we can see there are two important areas to consider:

  • How infectious it is, and
  • How controllable it is.

The first is inherent to the disease itself. The second, hugely dependant on countries resources and the social contracts populations are willing to make. Both appear to be a big deal. The R0 is higher than most things we're used to. The exponential implications of this are serious. And whilst it's been controllable, this has come at a huge cost. This in itself is a big deal. In fact, as isolation requirements drag on, economic damage increases. This leads many to question if it's worth it?