Unthinkable in 2019, the lockdown has been a major public health measure in Australia to reduce the impact of COVID. However, lockdowns take a toll on the population, and there is a limit to how long people and communities can maintain these behaviors.
While governments impose restrictions through policy, the real reduction in spread is due to changes in people’s behaviour. Our collective choices have slowed the virus and stopped it on several occasions – until the recent delta variant outbreaks in New South Wales and Victoria.
We have been modeling behaviors in Australia since April 2020 and how they relate to changes in the ability of the SARS-CoV-2 virus to spread COVID. Our understanding of how people have reacted to policy setting is the basis for Doherty modeling.
Concerns about “compliance fatigue” may make us question the role of lockdowns in the current outbreak. Is the exhaustion rule-bending or breaking? In fact, Australians have shown themselves to be resilient and adaptable.
Macro-distancing and Micro-distancing
During this pandemic, Australians have shown an impressive ability to change the way we interact with others.
In our analyses, we consider two major population behaviors that suppress transmission: macro-distancing and micro-distancing.
Macro-distancing is about the number of people we interact with, while micro-distancing is about our behavior when we look at people.
The two work together to reduce transmission at the population level. We monitor these behaviors using data from weekly anonymous nationwide surveys. We also collect data on the mobility of people collected by technology companies, including Google.
Read more: Doherty provides modeling update goalpost, but local insights will determine the game
transmission efficiency and effective reproduction number
We combine these behavioral data with data on vaccination coverage and our understanding of disease dynamics to calculate transmission potential (TP). TP measures how contagious COVID must be in the community on average. If it is more than one, we expect the virus to spread. If it is less than one, the virus should not be able to establish itself, even if it has originated in the community.
The TP is updated weekly for each state and territory in the Common Operating Picture. Where the virus is circulating, we also measure the effective reproduction number (Ref), which measures the actual rate of spread among currently active cases.
Where the virus is circulating, we want to take the ref down to one. And for Australia as a whole, we aim to get a TP close to one.
Read more: Relying on vaccination alone is not enough in NSW from 1 December – here’s what we need for continued independence
how the behavior changed
Over the past 18 months, the levels of macro- and micro-distancing behavior achieved under any restrictions have changed. According to our modelling, the first national lockdown saw the biggest change in behaviour. The Australians responded to the threat and we stopped the virus.
We have repeatedly observed low levels of admixture in our modeling – both macro and micro – in response to outbreaks and sanctions, at the height of Victoria’s second wave, and most recently in NSW, Victoria and ACT.
Outside the lockdown period, different regions of Australia see very different patterns. After the second wave, Victorians remained cautious, maintaining less shaking and micro-distancing behavior than anywhere else in the country. In contrast, those not on the eastern seaboard continued to shake more.
However, when the virus strikes and stay-at-home policies are in place, we all react equally. The infiltration of the virus into Western Australia and the Northern Territory in 2021 resulted in a drastic change in behavior.
Our behavior changes for reasons other than government policy. As our perception of risk increases, we naturally increase our distant behavior. We have seen an increase in macro- and micro-distancing behavior as cases rise, and sometimes even before stay-at-home measures are implemented. We have also seen shorter distances as the number of cases decline.
Has the behavior change led to the spread of the delta variant?
The emergence of the delta variant has fundamentally changed our ability to control COVID. The delta variant is almost twice as infectious as the parental strains since the beginning of 2020. The behaviors that stopped COVID in its tracks earlier in the pandemic can only slow its spread now.
Our modeling of distancing behavior and transmission efficiency allows us to test theories.
We might ask: if Delta was established and people behaved like they did in Victoria in August 2020 (during the second wave of the original COVID strain), could we control transmission? At that time, we estimated the transmission efficiency to be 0.56. Adjusting for delta by doubling 0.56 makes the number greater than 1, which means we will see an increasing outbreak.
The reverse scenario can also be modelled. Current practices in the Australian Capital Territory, New South Wales and Victoria will probably be sufficient to prevent transmission of the earlier COVID strain.
Although the case count is high this year, we are still reducing our contacts and slowing the spread of the virus as we did in 2020.
Why is lockdown not enough?
Overall measures of behavior do not tell the whole story.
Certain sections of the community are unable to work from home and are therefore limited in their ability to narrow down their contacts. The lockdown has not been effective in reducing transmission in some workplaces. So despite careful behavior we may still see rising caseloads.
It’s a pattern that played out throughout the pandemic.
In NSW, recent transmissions have occurred mainly among essential workers. In the Victorian Second Wave, the bulk of transmission was in residential aged care homes, where there was inevitable close contact between workers and residents.
Read more: ‘Are you double dosed?’ How to ask friends and family if they have been vaccinated, and how to handle it if they say no?
Signs of lockdown fatigue?
Illegal gatherings can lead to clusters of infection (as reported after the AFL Grand Final).
While these well-publicized events are one-sided, they are costly because they seed the virus into new communities. The outbreak in Victoria’s Delta is now bigger than it used to be.
Thankfully, these types of incidents, driven by minority individuals, do not reflect the preferences of the wider population. They do not reflect our collective ability to slow the spread of the virus.
Despite initial challenges, we are now on track to achieve world-leading vaccine coverage. We have already seen high vaccine coverage helping the NSW turn the pandemic around. Victoria is also not far behind.
Every vaccine administered makes outbreak control easier. And every choice we make about how we interact with others matters.