Our borders have been shut to non-citizens for about a week and despite being regularly admonished for being terrible at obeying confusing, constantly changing or poorly communicated new rules, the past few days have seen some signs of slowing in Australia’s COVID-19 numbers. Let’s explore this clear change in the pattern a little further.
A few quick facts
The average incubation period – the time from infection to showing symptoms – is about 5 days. The whole range is between 2 to 14 days.
Our national borders were closed to travellers from 20th March. As I write this, that deadline was about one week ago.
Most cases in Australia – nearly two thirds – have been introduced via infected travellers.
By my rudimentary calculations, we should now be seeing an impact on the case numbers. And it looks like we could be.
Are total Australian cases slowing?
For the past five days – the numbers have either increased by a smaller amount than the day before (23rd, 24th and 25th) or they have decreased compared to the biggest days (26th).
To be clear – this could be just a bump slowing the journey of a very long road. I’m not saying Australia is done and dusted or that we should relax even a little bit yet. In fact – seeing thing do nothing is exactly what we want! But this could be a sign that border closures have impacted what has so far been the biggest known source of COVID-19 cases; infected travellers arriving from overseas.
How sure are we about this local community transmission thing?
We have heard much about Australia having very little sustained or widespread local transmission of SARS-VoCV-2 out in the wider community, away from travel-related cases and their contacts. But until recently, testing mostly targetted those groups plus the elderly and those in a
We haven’t seen lots of new severe respiratory disease cases turning up in our hospital. Even if severe disease represents perhaps less than a fifth of COVID-19 disease outcomes, we’d still expect to see the number in hospital grow in proportion to any widespread local but noticed (or cryptic) transmission.
As far as I know, we haven’t seen that happening.
We also haven’t seen any spike in deaths. This one is a bit more problematic as death can take weeks to occur so there is an expected lag between a case being detected when ill, and that person dying if they do. A death today could have been from an infection happening more than a month ago. So we will probably see among the bolus of cases we’ve recently had, around 1% die (just going by one f the more common predicted and adjusted figures).
We’ve had cases in Australia since late January. As of today, we have 13 deaths and 3,177 cases – 0.4% of cases dying doesn’t suggest we had a lot of missed cases early on. But we do need to keep watching that as a lot of cases have occurred in a short and recent time.
Iran is reporting that 7.6% of cases have died, Italy 10.2%, Indonesia 8.7%, Philippines 6.3% and the United Kingdom at 4.9%. On the other end of the spectrum, the United States has so far seen 1.5% of cases die, South Korea 1.4%, Germany 0.61% and Singapore 0.29%. Of course, these could also swing upwards at any time, becoming worse if healthcare services become overwhelmed.
But these are the main reasons to think that unseen or cryptic spread isn’t happening to a large extent in Australia. Good news if true!
It will be happening to some extent because it has everywhere. But our new measures to prevent the entry of so many travellers into Australia should help keep numbers down, as have our rapid and flexible testing approaches. China has also now restricted travel into the country except by returning citizens. Perhaps we are all learning from each other.
The asymptomatic and presymptomatic conundrum
NOTE: I’ve been told in the past by those who look after asymptomatic cases (not ill but tested positive), that if you look hard enough, many will probably have a very short temperature spike, headache, feel a bit hot or unwell etc. The sort of thing that might not be recalled but could be noted at the time.
The rest are in a presymptomatic phase; they will go on to develop illness of varying severity.
We know it is possible for those in either group to host infectious virus in their airway, so there is some risk for transmission. But whether they are a big source of unseen or unnoticed spread of SARS-CoV-2 still seems hard to nail down in Australia.
With more relaxed testing guidelines (see below), we’ll soon learn whether Australia has missed a significant portion of infections, or has remained ahead of the virus. Right this minute, it looks more like the latter.
This isn;t the end of things in fact, if this trend is real, its happening because of some of the most unfamiliar, unexpected and fairly surreal changes made to our way of life. These changes will need to stay in place for many weeks or else that peak will just bounce straight back up. It may still bounce up if we do start to see local transmission take hold.
Everbody’s eyes should be on these daily bars – we want them to keep going down. At the very least, to stop going up.
Time will tell. In the meanwhile – wash your hands more than you do, don’t touch your face until you do and stay physically – but not socially – apart from each other.
- Charting the COVID-19 spread in Australia
- Evidence of SARS-CoV-2 Infection in Returning Travelers from Wuhan, China
- National Cabinet Update. Media release 26 Mar 2020 Prime Minister
- China reports deeply disturbing coronavirus development
- Estimating the asymptomatic proportion of coronavirus disease 2019 (COVID-19) cases on board the Diamond Princess cruise ship, Yokohama, Japan, 2020
- Clinical characteristics of 24 asymptomatic infections with COVID-19 screened among close contacts in Nanjing, China
- Presumed Asymptomatic Carrier Transmission of COVID-19
- Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus (SARS-CoV2)