Through this pandemic, scientists have learnt a lot and one of the areas where the advice has changed is on the wearing of face masks.
What's the advice now?
It's not just advice. It's an instruction.
The federal government says: "Everyone in the state of Victoria must wear a face covering whenever they leave home unless an exemption applies.
"People in NSW should consider wearing a face mask in situations where physical distancing is not possible."
The ACT government has not ruled that masks must be worn. It's watching the situation in NSW to see if the outbreak gets nearer to Canberra.
In Victoria some exceptions are allowed, including:
- Infants and children under the age of 12 years.
- A person who is affected by a relevant medical condition, including problems with their breathing, a serious condition of the face, a disability or a mental health condition.
- Persons who are deaf or hard of hearing, where the ability to see the mouth is essential for communication.
- Persons whose professions require clear enunciation or visibility of their mouth. This includes teaching or live broadcasting.
- Professional sportspeople when training or competing.
And the science?
The science is unclear. There have been studies which seem to show a fall in infections as mask-wearing rises but that may be because people who start wearing them do so because they are worried about COVID-19, and worried people also keep their distance from others and wash their hands more.
There is definitely evidence that infected people wearing masks cuts the risk of them infecting others.
But the World Health Organisation says: "There is limited evidence that wearing a medical mask by healthy individuals in households, in particular those who share a house with a sick person, or among attendees of mass gatherings may be beneficial as a measure preventing transmission."
Why wear a mask then?
We're all in this together and we have an obligation as good citizens not to spread a highly infectious disease.
The official advice comes from well-meaning, highly intelligent scientists whose expertise is more reliable than nonsense on the internet.
The evidence is that mask-wearing does slow the spread of infection even if it doesn't offer complete and certain protection to mask wearers.
Many, perhaps most, people who are infected don't have symptoms so they may go around infecting others without realising that they themselves are infected.
The best recent advice comes from the Royal Society which was founded in the 1660s "to recognise, promote, and support excellence in science".
It says: "Evidence continues to accrue that masks, including cloth masks, prevent onward transmission of infection."
And it adds: "New evidence finds that the use of clear plastic face shields can prevent onward transmission of droplets and aerosols (tiniest droplets).
"This addresses concerns from individuals and communities who/that cannot use masks, for example, deaf people and individuals with breathing disorders."
What about Sweden?
Sweden has a low rate of infection but Swedes don't tend to wear masks.
They have had what's called "lockdown-lite". Large gatherings were banned but schools remained open. Restaurants stayed open but with strict social distancing.
The medical authorities there have hammered away at the absolute necessity for social distancing and frequent hand-washing - and Swedes seem to have followed the advice.
Holland has taken a similar course. The government said masks wouldn't be compulsory. It fears that mask-wearing might not be that effective in itself but also breed a dangerous complacency about social distancing and hygiene.
So what should we do?
Professor Peter Collignon of the Australian National University Medical School told The Canberra Times that masks "have value", but they were only the fourth or fifth line of defence, behind, particularly, keeping your distance from other people and frequent hand washing.
He thinks we should wear masks where there is significant community infection (like Victoria and parts of Sydney) and be ready to wear one elsewhere in confined spaces with lots of people (like a crowded bar or shop).
And if someone is ill in your family, wear a mask. Professor Collignon thought people sometimes falsely assumed that they couldn't catch COVID-19 from a friend or family member.
How should we wear masks?
It's important to get it right. If you don't, wearing a mask may be pointless and you will be subjecting yourself to minor discomfort to no purpose. You may also be deceiving yourself that you are protected when you are not.
"As doctors, we had to start using masks during our training," he said.
"I can tell you it's something that you do get used to quickly. It just becomes a natural part of what you're doing.
"You need to take care in putting on and removing your mask to minimise your risk of any exposure to COVID-19.
"That means washing your hands before putting a mask on and straight after taking it off.
"It means making sure it covers your mouth and your nose - don't let it hang around your neck.
"If your mask is wet it won't be effective so you need to change it if it's a disposable mask, or wash it if it is a cloth reusable mask.
"And please make sure you don't touch the front of your mask either whilst wearing it, or taking it on or off."
What kind of mask?
There are surgical grade N95 respirator masks on the market but they are expensive and can't be used repeatedly ($4.95 each at one popular office supplier).
Cloth masks are cheaper and more practical.
A study in the United States concluded: "The best-performing design was constructed of two layers of high-quality, heavyweight "quilter's cotton" with a thread count of 180 or more, and those with especially tight weave and thicker thread such as batiks.
"A double-layer mask with a simple cotton outer layer and an inner layer of flannel also performed well.
"The inferior performers consisted of single-layer masks or double-layer designs of lower quality, lightweight cotton."
To recap ...
The best advice is that masks help but don't rely on them. Keeping your distance and washing hands frequently are the really essential bits of advice.