COVID-19 Down Under: Australia Catches a Third Wave

By Jennifer Lang and Karen Cutter

COVID-19 Actuaries Response Group – Learn. Share. Educate. Influence.


For much of the pandemic, Australia, along with its neighbour New Zealand, has been relatively successful in protecting its population from the health impact of COVID-19. This has been achieved through maintenance of very tight border controls, strict lockdowns during periods of outbreaks, and a comprehensive test and trace system to identify both upstream and downstream contacts where cases have been identified.

We explore some of the reasons for Australia’s success, together with some insight into the ability of the virus to spread which is only possible to gain in an environment where very few cases exist. Recently, the Delta variant has resulted in a more rapid spread, with renewed lockdowns insufficient up against Delta’s high R0 to drive cases down to zero again. With a much smaller proportion of the population having derived natural immunity, and vaccination levels relatively low, the country faces an uncertain position as it considers its next steps in dealing with the continuing threat from the virus.

Australia – a Federation of States

Australia is a federation of states – the federal government taxes the population and makes budget decisions (and lots of other things), and the states run hospitals, schools and police.

That means that even though Australia’s federal government often looks to the US and the UK philosophically, when the federal government was toying with “living with the virus” back in March 2020, the two biggest states – New South Wales (NSW) and Victoria (which include Sydney and Melbourne) – dragged the country into a full lockdown and shutting of the international borders. It helped that our neighbour, New Zealand, did the same thing a few days before.

Australians sometimes wonder what the point of the states is, but in times like these, the structure provides diversity of decision making. Many of us have also realized just how much of the day-to-day service provision is run by the states. In many instances, the federal government has wanted a certain action, and the state governments, as service providers, have followed a different path. This has, unsurprisingly, created much tension between the various levels of government, even when the political parties are aligned.

Zero-COVID Aim

Once the country locked down, with everyone entering the country required to spend fourteen days in state government-run hotel quarantine, community transmission was basically eliminated by May 2020.

Hotel quarantine isn’t perfect though – around 1-in-100 positive cases have resulted in a leak out of quarantine and have infected people in the community[1]. And with the Delta strain, the frequency of leaks from hotel quarantine has increased as shown in the graph below (noting that the caps on international arrivals were cut in half in May 2021).

These leaks are believed to have come about through:

  • Infections in airport workers
  • Poor ventilation in the hotels themselves resulting in transmission between hotel rooms
  • Inadequate PPE and/or breaches of infection control resulting in doctors, nurses, security staff, cleaners and patient transport staff becoming infected.

Most of the leaks have not gone on to cause major issues and onward transmission has been stopped through a combination of rigorous contact tracing and/or short lockdowns (3-5 days duration). The short lockdowns give contact tracers a little breathing room to enable all close contacts of cases to be identified, tested and put into home isolation.

However, leaks from hotel quarantine in late-May 2020 resulted in the state of Victoria having a second wave of the virus, which was suppressed down to zero with a very harsh lockdown (including, at some stages, overnight curfews). And now in September 2021, the state of NSW is locked down amidst a third wave of the Delta virus that has also spread to other states, resulting in the lockdown of Victoria and the Australian Capital Territory (ACT) (and neighbouring NZ) as well.

We can imagine that the Australian response to (relatively) small numbers of COVID cases may seem a little over the top compared with what is happening in much of the rest of the world. But from Australia, watching the rest of the world for much of the last 18 months, from a place where life was continuing mostly as normal, makes the possibility of getting to zero cases again pretty enticing. Australia’s health system is good, but that is also the case for many other countries where the system has been overwhelmed with COVID cases. And the distances involved mean that sharing hospital infrastructure across this vast nation (or even between country towns) is not practical. While much of our population lives in large cities on the east coast, plenty of Australians live in rural areas or smaller towns that are a long way from large hospitals with lots of ICU capacity.

Closed Internal Borders

As well as closing our international border, states have closed their borders to each other. For much of the last eighteen months, many Australians have been unable to leave the state they live in. Internal borders close quickly in the event of an outbreak in another state, and are slow to reopen. In some cases, internal border closures have been easy to manage as the borders between states are natural borders (e.g. Tasmania is an island, and there is a large desert separating Western Australia from the rest of Australia). In others, there are large population centres on the borders which have created many difficulties for the residents of those communities.

Closing of internal borders is also not perfect. There are exemptions for essential workers, on compassionate grounds, and also if moving interstate. It seems like whenever borders are closed, and even while case numbers in Australia are low, there always seems to be a breach!

This map shows the outbreaks in Australia from May 2021 until mid-July 2021 (prepared by @dbRaevn who you can find on Twitter).

We can see that the Sydney outbreak (blue), caused cases in Perth, Melbourne and Brisbane, with cases mainly from returning residents, but also from the removalists of a family who were moving to Melbourne, a flight attendant, and travellers who entered Queensland when they should not have.

On the map also are cases related to the Granites Gold mine (orange) in the Northern Territory. These cases started with a “fly in, fly out” miner from Melbourne. The only way for this miner to get to his workplace was to fly to Brisbane and then on a charter flight to the mine the next day. At the time, anyone entering Queensland from Victoria was required to stay in hotel quarantine for 14 days, so the miner needed to stay in hotel quarantine overnight while waiting for his charter flight. During his stay, he unknowingly contracted the virus from an international traveller in the next room. He then went to work at the mine and passed the virus on to other miners, who then returned to their homes in Darwin, Adelaide, Brisbane and Sydney. This example shows the difficulty of completely suppressing the virus whilst movement occurs, as the control in place to limit spread (quarantine) actually resulted in the outbreak occurring.

Negative Excess Deaths

The full suite of non-pharmaceutical interventions has meant that, in contrast with much of the rest of the world, the population death rate has been better than normal. We entirely missed our normal winter flu season in 2020 (zero deaths, instead of the usual around 600) and the flow-on impact of the lack of many respiratory diseases reduced the death rate from quite a few other causes – chronic lower respiratory disease and dementia being the most prominent.

In total, around 4,000 fewer people than expected died in Australia in 2020, a negative excess of 3%.

For anyone interested in more detail, you can find our full paper here.

Insights from Zero Cases and a Strong Testing and Tracing Regime

When there are very few to no cases in the community, a lot more can be learned about the virus. Here we give a few examples of statistics that would be unavailable in jurisdictions with more virus circulating.

1.      Asymptomatic Testing

Hotel quarantine has been occurring in Australia for more than 12 months. Each person is tested on entry, part way through their stay (if symptomatic), and prior to exit after 14 days. The data from this comprehensive testing process provides extraordinary insights. For example, this analysis from December 2020 shows that the day 10 test still identifies a material number of positive cases with no symptoms.

2.      Insights from Contact Tracing

Except for during the two big waves, the contact tracing system around Australia has been comprehensive. With every positive case, contact tracing is undertaken to work out both where the case contracted the virus (upstream tracing) and who they may have passed it on to (downstream tracing). Every case is interviewed and asked where they have been. This is cross-checked against QR code check-ins (mandatory at all public places), banking and phone records. The locations visited by a case are published and other individuals who have been to those sites are contacted and tested (and for some high-risk venues, are required to isolate for 14 days). In some instances, serology testing is used to determine when a case was infectious. All cases that can be are genomically sequenced to confirm the epidemiological links are correct and there are no missing chains of transmission.

This leads to situations where a single person’s movements across a city are known by looking at the public exposure sites which can lead to some quite funny urban legends. For example, “barbeque man” visited four different shops selling barbecues and then a butcher. The presumption was that he was shopping around for a good deal on a barbie, had success, and then bought a steak. In reality, he was a businessman who was looking to purchase a chain of barbecue shops!

It also leads to fantastic information about how the virus actually spreads, as all cases and transmission mechanisms can be identified. The contact tracers do not stop their work when two cases are discovered to have been at the same venue. They use CCTV footage where available to see where the two people may have interacted, to pinpoint the actual transmission event. The outbreak map below (by @dbRaevn) shows the beginning of the NSW third wave (delta strain).

S1 is the index case in the cluster, and was a limousine driver for international air crew. Despite the fact that all quarantine workers are supposed to be vaccinated and follow PPE requirements, this driver was unvaccinated and did not wear a mask. Note that at this time, while quarantine workers had PPE requirements while at work, there had not been cases in the community in Sydney for five months. As such, mask wearing in public places was not mandatory, nor usual practice for most of the population.

The limousine driver passed the virus on to:

  • his wife (S2)
  • a woman who dined at the Belle Café (S3) at the same time as him. There was a lot of interest in S3 as she was seated outside in the café, while the man was seated inside. There was no CCTV footage, so the crossover of the two people could not be observed, however it is thought that the woman may have crossed over with the man when paying her bill inside the café.
  • A man (S5) who shopped at Myer (a department store) within Westfield Bondi Junction (a large shopping mall) at the same time as the limousine driver. CCTV footage showed that the two men were in the menswear department at the same time, but some distance from each other. They were only in close proximity to each other at one point when they walked past each other
  • A woman (S6) who lived close to Westfield and regularly walked through the mall. No transmission event between the woman and limousine driver has been established. This woman passed on the virus to her husband and all of their four children.
  • A man (S7) who was also at Westfield, who then transmitted to his wife (S8).

S15 is interesting. This woman worked at a nail salon in Westfield, but no link to the limousine driver could be found at the time of her diagnosis. Later it eventuated that there was a “missing link” – someone who contracted the virus elsewhere, and who subsequently was a customer at the nail salon. It is these unlinked cases that cause the public health team sleepless nights.

S15 also went to a family birthday party while infectious, where the guests ranged in age from young children to older adults. Of the 40 guests at the party, eventually 27 were diagnosed with COVID.

This detailed contact tracing in a low-COVID environment allows studies such as this one, looking at transmission in a church environment. It identified the possibility of transmission from quite a distance, if the ventilation was poor, and was a key piece of supporting evidence for airborne transmission of COVID19.

We are hopeful that the Australian experience will result in further studies of this kind.

What Went Wrong?

We now have a third wave of COVID19 hitting Australia. While the outbreak started in Sydney, it has now spread to regional NSW, the ACT and Victoria – all of which are currently in strict lockdowns. There have also been incursions into Queensland (that have been quashed) and the outbreak in New Zealand can be traced back to a person in their hotel quarantine system who had arrived from NSW.


So why didn’t the excellent contact tracing in Sydney get on top of the virus? There are a combination of factors, but the main reason is because it has been almost impossible to get ahead of the much more infectious delta variant. As is the case around the world:


  • The secondary attack rate of the delta strain has proven to be much higher than for previous strains; health officials have found that by the time the first case in a household is diagnosed, they have already transmitted to everyone else in their household. For previous strains, only around 30% of household members were positive.
  • the transmission events described earlier in relation to the NSW outbreak between S1 and to S3, S5, S6 and S7 were the result of “fleeting contact”. For previous strains, transmissions of this nature had not been observed.
  • Transmission between children is occurring much more frequently. Previously outbreaks in childcare centres and schools were mainly the result of teachers transmitting to children rather than vice-versa, and with very little transmission between the children themselves. Infected children were generally not then onward transmitting in their households. Now, with Delta, outbreaks in both primary and secondary schools in Queensland, the ACT and Victoria all point to much more transmission occurring between children, who are then also passing the virus on to their parents and siblings.
  • While outdoors remains much safer than indoors, we may have documented evidence of outdoor transmission occurring at an Aussie Rules football match in Melbourne. A COVID-positive person attended a match and transmitted to several people there. CCTV footage reveals that some of the people who caught COVID at the match came close to the person while entering the grounds, at food/beverage outlets, and in the bathrooms. However, there were some cases where close proximity could not be established and the seating allocation suggested outdoor transmission.

When up against the much more infectious variant, there is no room for gaps in the contact tracing. And there were a few gaps – even an excellent contact tracing system is reliant on full information from those who are diagnosed cases. As a result, the virus ended up in the less affluent areas of Sydney, where it has proven much more difficult to quash given that this is where many of the city’s essential workers reside (they still need to go to work), households tend to be much larger and comprised of multiple generations, English is a second language for a large proportion of the population making messaging much more difficult.

The combination of a much more infectious disease, and a largely unvaccinated population, means that even quite tough lockdowns are not reducing spread adequately. Australia on 11 September 2021 has around 2,000 cases a day (1,500 in NSW), with an implied doubling time of 20 days (though this is gradually reducing). It is a race with the vaccination process, but at only 33% of Australians fully vaccinated, it is going to take some time for Australia to be able to remove lockdown restrictions without a very high risk of the health system being overwhelmed.

Why are so few Australians Fully Vaccinated?

The less positive outcome from such long periods with no cases in the community is that the vaccination progress has been very slow. This graph below shows that Australia is well behind vaccination rates of comparable countries, even Singapore, which has also had few cases and deaths.

This is through a combination of slow purchasing, and a relaxed attitude to the rollout of vaccinations from both government and the population – the very rare complications from Astra Zeneca, for example, have led to many people choosing to wait until a Pfizer dose might become available.

The slow rollout has become a political issue, which perhaps explains why there is no publicly available good granular data about who has been vaccinated; which in turns makes it difficult for the wider community (such as community leaders from immigrant groups with poor English, and Aboriginal health services) to support the rollout out in their own communities.

Australia’s identified cases per 100,000 population are about 2% of the UK (and the reality is probably a lower percentage, given the testing in Australia has not been under as much stress). So the Australian population is a long way from herd immunity, even further away than the vaccination rate would suggest.

The pace of vaccination has picked up with the recent outbreaks, although supply still remains an issue.

Where Next for Australia?

For much of the last 18 months, the goal has been zero-COVID. But this cannot be the goal forever when clearly COVID will not be eradicated world-wide. The health teams have concluded that the current waves in NSW and Victoria cannot be eliminated with lockdowns – vaccination has to be the way out. Australia will need to reopen to the rest of the world once we have sufficient vaccination coverage, and exactly when and how that happens (and how and when the states of Australia that still have zero-COVID open to the rest of Australia) is still a work in progress.


12 September 2021

[1] 39 breaches from hotel quarantine from 3,620 positive cases in the quarantine system –

About henry tapper

Founder of the Pension PlayPen,, partner of Stella, father of Olly . I am the Pension Plowman
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