We have seen how dangerous the Covid-19 virus is and the damage it can do, and around the world we have learnt the hard way that we can’t drop our guard.

It is important, however, in recognising the threat it poses, and in seeing what might be yet another breach of hotel quarantine in Australia, that we don’t ascribe magical powers to this virus. To infect a person it has to do something very straightforward: it needs to be physically transferred from one person to another.

It can do this in a number of ways.

Most well understood of those ways is through the expulsion from the respiratory tract of an infected person as large droplets. These droplets in most situations travel only a short distance from the person who produces them. They can land directly on a person to infect them, or they can land on a surface and subsequently transferred when they touch the surface and then touch their eyes, nose or mouth.

The spread via large droplets is easy to understand and relatively easy to combat. You can do this by keeping people away from each other, washing hands, and using simple physical barriers like surgical masks.

Where there is a bit more uncertainty is the ability of the virus to be spread by small droplets, or aerosols, which have the potential to travel and infect at larger distances. Combatting these smaller droplets is more difficult, since apart from being able to travel larger distances as they surf air currents, they are also better able to evade simple barriers like surgical masks at closer distances.

Much of the discussion about the role of airborne transmission and its importance in hotel quarantine has been distracted by issues that simply aren’t very relevant. What matters is that airborne transmission can happen. Although it has taken some time, it is welcome news that the US Centers for Disease Control and Prevention and the World Health Organization have updated their guidelines to recognise officially that airborne transmission occurs.

The main distraction concerning airborne transmission and hotel quarantine has been a disagreement over the importance of the airborne transmission route.

Any disagreement over whether it is a major transmission route or not is generally not helpful. Transmission is very much context-dependent. You can’t talk about transmission of Covid without speaking about the environment. We know that airborne spread is more likely to happen in indoor environments where there is poor ventilation – places like hotels.

The fact is airborne transmission can occur, and its risk of occurring is increased when indoors with inadequate air circulation. This risk is heightened the greater the number of infected people in close proximity.

The importance of the airborne transmission route is even more pronounced relatively speaking when you have already taken effective measures to combat close person-to-person spread through large droplets. You can see where I am taking you here: this looks very much like hotel quarantine.

The best analogy is a ship that isn’t completely watertight. If the ship is 95% watertight, all that matters in keeping the ship afloat is addressing the 5% of the issues that are letting water in. The 5% that is not watertight represents 100% of the problem that needs to be addressed. If you can address this weak point, you can prevent the ship from sinking.

So it doesn’t matter what the relative contribution of airborne transmission is in terms of all transmission. All that matters is that in the high-risk hotel quarantine environment it is the one route of transmission that is not being fully and consistently addressed, and therefore it is where the problem lies in sealing this system against leaking.

If we accept that for now hotel quarantine is going to be the first line of defence for Australia and we are going to be needing it for some time – which many of us would prefer is not the case – then we need to commit to doing everything we possibly can to prevent transmission by the airborne route. Anything less than tackling this issue head on – and fully – should not be accepted.

What is needed is to ensure people wear the right type of masks and that greater attention is paid to ventilation in hotel quarantine. It may require some effort but the benefits of having a hotel quarantine system we have more trust in are massive.

The virus is a formidable foe, but it is not magic. It should be within our capabilities to make hotel quarantine much safer.

Associate Prof Hassan Vally, department of public health, La Trobe University

This content first appear on the guardian

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