by MERLIN CROSSLEY

Imagine a heavy freight train accelerating straight down a mountain side. One would hope the modern marvels of science would be available and we’d have a braking system that was computer operated by high tech artificial intelligence (e.g. anti-viral drugs and a vaccine). But, actually, the only brakes we’ve got are old fashioned hygiene (washing your hands) and barriers (border controls and physical distancing). These are the brakes – the moment we relax the train will start accelerating again.

There are strong arguments for pushing the brake pedal to the floor – now. If we manage to stop the train (no new cases for four weeks) then we can gradually open up the economy within Australia and open up to other countries who are progressing towards national eradication – New Zealand and perhaps China.

Modelling shows we are on track and we are probably talking weeks or a few months, not years – provided we maintain current high levels of physical distancing.

Some say that asymptomatic spread and mild cases make it harder to eradicate the virus via physical distancing, but physical distancing will also reduce spread from asymptomatic people. In fact, it is the other strategy – adopted by South Korea, Japan, and initially by Singapore – testing, identification, contact tracing, and isolation, that is hampered by the presence of asymptomatic carriers because the lack of symptoms makes it so much harder to find carriers and isolate them before they spread the virus to others. You have to test extensively. Helpfully, physical distancing helps not only in combating symptomatic and asymptomatic spread but also in improving the chances of identifying contacts, whenever carriers are detected. Singapore recently increased physical distancing measures, as has Japan.

Others say that the train is our economy and we’ve got to get it moving again. It may be that there are some frail and elderly people lying on the tracks ahead and clinical staff with them, but closing the economy will cause other hardships and have knock on health impacts too. There is a cold logic to this but I am more convinced by the arguments that national eradication is the quickest way to get the local economy moving again. I think we should go all out for eradication in order to allow the economy to restart with confidence – the alternative is stop-start.

Another idea is to ease off on the brakes and attach a few hospital carriages to our train and then just let it trundle along. We should certainly prepare stocks of Personal Protective Equipment (PPE) and reconfigure hospitals to protect health workers, and ramp-up testing, so we test all health workers and as many people as we can – but we will never be able to test the entire Australian population, so unless we get to elimination, easing our foot off the brakes will always carry risk.

The talk of herd immunity is fading because it looks like even in places where the virus has spread at high levels less than 5  per cent of people have been exposed – and this has always been associated with unacceptable death rates. It is estimated that one needs 60 per cent or more people to be immune to achieve herd immunity – one can scale up from existing numbers to work out how many deaths that would mean. Plus, no one is sure how many of the 5 per cent of people who have contracted the virus will have acquired good immunity, or how long their immunity will last. Sadly, immunity to known corona viruses seems to last months rather than for many years.

In Europe, some countries, perhaps Sweden, have attempted to protect those most at risk (e.g. the elderly) but it has proved impossible to segment society into risk groups. The virus has found its way into aged care facilities, and, of course, into hospitals, and death tolls are high.

But is it possible to let the train roll while we develop those high-tech anti-virals? There are hundreds of trials in progress and existing drugs, with known safety profiles (such as remsdesivir that inhibits viral replication) are being tested for efficacy. Some drugs will help reduce symptoms and the death rate, but it is unlikely that any of these first generation drugs will actually cure this infection. Effective drugs or combinations of drugs have in a few cases been developed against viruses, like those that cause hepatitis or HIV, but it has taken years of work to make and validate these reagents. I’m optimistic, about scaling up humanised monoclonal anti-bodies (based on natural human anti-bodies from patients who have overcome the infection) but these things will take time and will not end the epidemic.

Similarly, while I’m sure there will be vaccines, the time frames for safety testing, scale up, and delivery across our population, and the extent of immunity and length of protection, are impossible to predict.

You will know that there is no vaccine for the common cold – and corona viruses cause common colds (they are apparently the second most common cause of colds, with rhinoviruses, parainfluenza and adenoviruses also contributing).

You will also be aware that once you have had a cold, you are not protected from getting another one in the future. The data I have seen to date – that macaques have a good immune response to the virus that causes COVID19 – makes me optimistic that at least some of the many, many labs working on a vaccine will succeed, but this is a trial and error process of educated guesses, albeit from some of the smartest people in science. We need surer strategies – and hygiene and physical distancing are, believe it or not, extremely effective provided the vast majority of people practise them.

If Australia or New Zealand can keep the spread down to the current rate for a bit longer then we will bring the train to a halt and will be able to say our islands are clean and our local economies can resume. Of course, we still can not open our borders until a vaccine or therapies are developed but I do not think any of us are expecting much travel for a while.

If we don’t manage eradication, we will face stop-start restrictions, yo-yoing and zig-zagging in one place after another. One hopes future restrictions (if we need them) will be more locally targeted (as we are now seeing in north western Tasmania) than the nationwide shutdowns we are now experiencing, but the way this virus spreads, even from those with no or minimal symptoms, will make it very hard to contain – even if we ramp up testing and contact tracing.

So, I for one, am very pleased that the PM has indicated restrictions will stay in place for at least a few more weeks. During that time we should listen and learn to see what happens if other countries take their feet off the brakes. They may think they have passed the peak but in reality they have just gone over the first hump in what could be a nauseating roller coaster ride.

Please note – I am not a clinician or epidemiologist, but am a molecular biologist, whose first degree was in microbiology.  I am active in science communication and note that across the world debates about strategies related to COVID19 are emerging. My hope is that extensive reasoned debate here we will help ensure we find the best way forward.

Merlin Crossley is DVC E at UNSW. His Crossley Lab blog runs weekly in CMM