# Scott Morrison has said we'll face at least 6 months of disruption. Where does that number come from?

• Written by Joel Miller, Senior lecturer, Applied Mathematics, La Trobe University

Scott Morrison yesterday warned Australians will face at least six months of disturbance to our day-to-day lives as we navigate the coronavirus pandemic.

Social distancing measures such as restrictions on large group gatherings and events won’t just be in place until next week or the week after.

But where does that six month number come from?

It’s a combination of modelling and simulation using observational data from the COVID-19 pandemic worldwide, and historical data from past pandemics.

Read more: Explainer: what is herd immunity?

## Pandemics past

By way of comparison, the H1N1 influenza pandemic reached Australia in early May 2009 and finally petered out five to six months later.

This was because of seasonal changes as well as more and more people becoming immune to the infection (that’s the concept of herd immunity).

The Conversation, CC BY-ND Mathematical modelling Based on observed early growth rates, in the absence of any containment measures, we would anticipate COVID-19 to have a similar epidemic curve to H1N1. We can predict this using disease parameters estimated from Chinese and European data and a highly simplified mathematical model. The typical infected person causes about 2.5 new infections (this is called the reproduction number, or R0). The Conversation, CC BY-ND Without any intervention, the epidemic would grow until depletion of susceptible people slows the growth. The prevalence would start to fall when the susceptible population reaches what’s called a critical fraction, 1/R0. Once we pass this threshold a person with COVID-19 will only transmit the virus to less than one other person (because fewer people remain susceptible to infection). For a population of 25 million like Australia, this would require 15 about million infections. COVID-19’s observed doubling time has been about four days. That means every four days the number of cases has been roughly double what it was four days prior. We would calculate it takes about three months for one infection doubling every four days to cause 15 million infections. After the peak, we expect the total time to drop to be about the same as it took to rise. This gives a crude prediction of six months. Read more: How to flatten the curve of coronavirus, a mathematician explains Since we’re presumably partway into the epidemic, we might expect less than six months remaining. However, reality introduces many adjustments to this: the doubling slows down as we approach the peak, there is variation in individual behaviours, the geographic structure of Australia will influence the spread, and social distancing will have an impact. Thankfully, these adjustments significantly lower the predicted number of infections and the predicted peak prevalence, while the duration increases. Computer simulations To make our model more realistic we turn to computer simulations. These simulations draw on sources like census data and transportation networks to predict how disease would spread through a population. When we introduce interventions like those Scott Morrison has announced, our simulations show us COVID-19 infects fewer people and has a lower peak, but it lasts longer because it takes longer for immunity to build up. This is called flattening the curve. Flattening the curve is another way of saying slowing the spread. The epidemic is lengthened, but we reduce the number of severe cases, causing less burden on public health systems. The Conversation/CC BY NDIn the case of COVID-19, we must intervene and do so aggressively. We cannot wait for herd immunity to develop. Unlike the H1N1 pandemic, where Australia only reported 191 deaths, COVID-19 threatens to overwhelm our health system many times over. Interventions like social distancing, by facilitating fewer infections, can give us time to obtain more ventilators and other essential equipment, and develop improved control strategies. These might rely on new phone apps for contact tracing, or increased testing, for example. If these measures are effective enough, perhaps we can drive the reproductive number below 1 and then progressively relax interventions while keeping our hospitals below capacity. At the very least, the government’s advice on social distancing will flatten the curve and extend the epidemic so more patients arrive at hospitals that have capacity to treat them. We’ll need to have these measures in place for at least six months. There are many uncertainties, but I’m hoping for a long-lasting epidemic. Read more: How do we detect if coronavirus is spreading in the community?

Authors: Joel Miller, Senior lecturer, Applied Mathematics, La Trobe University

Coalition maintains Newspoll lead federally and in Queensland; Biden's lead over Trump narrows

arrow_forward

How the shady world of the data industry strips away our freedoms

arrow_forward

20 year old Aussie marketing genius helping billion dollar household brands

arrow_forward

### Politics

#### Did BLM Really Change the US Police Work?

The Black Lives Matter (BLM) movement has proven that the power of the state rests in the hands of the people it governs. Following the death of 46-year-old black American George Floyd in a case of ...

a Guest Writer

#### Scott Morrison: the right man at the right time

Australia is not at war with another nation or ideology in August 2020 but the nation is in conflict. There are serious threats from China and there are many challenges flowing from the pandemic tha...

Greg Rogers

#### Prime Minister National Cabinet Statement

The National Cabinet met today to discuss Australia’s COVID-19 response, the Victoria outbreak, easing restrictions, helping Australians prepare to go back to work in a COVID-safe environment an...

Scott Morrison

#### 20 year old Aussie marketing genius helping billion dollar household brands

Australian digital marketing agency, Co Media, founded by 20 year old marketing genius Lucas Cook, is making its mark on the world stage by gaining a number of high profile clients and quickly b...

News Company

#### 5 Reasons to Choose Pipe Relining

There’s nothing like a damaged pipe to stress you out and keep you up throughout the night. Depending on the extent of the damage, a pipe repair can be a complicated and time-consuming process. ...

News Company

#### Reinventing The Outside Of Your Office

Efficient work is a priority in most offices. You need a comfortable interior that is functional too. The exterior also affects morale. Big companies have an amazing exterior like university ca...

News Company

# News Company Media Core

Content & Technology Connecting Global Audiences