Or was it that the marketing campaign designed to foster a sense of communal social responsibility, particularly towards senior citizens, and focused on promoting social distancing, handwashing and reducing the risk of shedding and spreading coronavirus was less than the optimal approach to galvanising and changing the behaviour of young people? That's not necessarily to suggest that the advertising campaigns have been a complete failure, because millions of Australians have heard and are abiding by the messages being sent out by the public health authorities. But it did not seem to get the buy-in from younger people, anymore than angry denunciations by the Prime Minister, or shaming efforts by television broadcasters.

Forty years ago, Australia faced another public health crisis - and, again, initially with limited "buy-in" from a good many smug Australians. It was the HIV virus, and AIDS - which at that stage had only very limited treatment options. A former senior public servant, if one still engaged in public life, spoke to me this week of the problem of getting the public interested and concerned enough to conscientiously change behaviour. Many Australians might have empathised in principle with the victims - mostly homosexuals, intravenous drug users or haemophiliacs - but did not see themselves as being at great risk. They agreed intellectually that lifestyle changes were called for, but lacked a strong emotional response or much in the way of a sense that they needed to change too. Then came the Grim Reaper ads - arresting, shocking, and, on all of the evidence, very effective. Australian public authorities led the world in dealing with AIDS in the population, not least by involving and engaging with Australians who were most at risk.

With COVID-19 and younger people, the relationship between the risk of mild or asymptomatic conditions and the terrible suffering and high mortality among mostly very elderly Australians seems too remote. A different approach is needed, one which brings the risks home to the people whose behaviour needs to change.

We know now that coronavirus produces acute conditions particularly among people with compromised immune systems. Most people associated this with age. But there are many younger people in the community with compromised systems.

A young person being casual about the risk of coronavirus infection is a threat to the health of a person, young or old, undergoing chemotherapy for cancer. That might be your best friend, or your best friend's mum. A woman who has suffered from anorexia or bulimia is at enhanced risk. So is anyone with diabetes. Or any of the autoimmune diseases - such as lupus, multiple sclerosis or rheumatoid arthritis. Smokers and heavy drinkers are at higher risk. But so are people with asthma, eczema, hay fever and people who were allergic to particular foods. Add to that a raft of people with chronic respiratory conditions, including, particularly in children, ear disease, and those with more acute ones, including colds and flu. People who have had recent surgery. And malaria - no longer a major problem in Australia, but often to be seen at our door, and with symptoms, including fever, remarkably like a COVID-19 presentation.

A typical fit Australian woman or man - a very likely candidate for casually picking up the virus from a chance encounter with someone exhibiting no obvious symptoms, or nothing more than a cold, and then not themselves developing any condition, might not be in regular attendance at an aged persons home. There is a very good chance that this person will have been completely unaware of the transfer, which may have come from some surface both had touched. There's a good chance that this person will not develop any symptoms of having picked up the virus, or will not consider that she has COVID if she gets mild symptoms. If, of course, she suspects the condition, but does not know where she got it, she might present at a testing station and be rejected for actual testing - unless she had recently returned from abroad, or could show she had been exposed to someone already identified as a carrier. And even if she were tested and told she was a carrier, she would be sent home for a fortnight and warned not to associate with others.

But innocently or not, asymptomatic or only mildly suffering, this woman or man is, we think, actively shedding and spreading the coronavirus, whether directly to others by physical contact or by leaving the virus on surfaces. This person may not have much direct contact with the very elderly, but she, or he, is much more likely to be in casual contact with diabetics, smokers or people with multiple sclerosis - people whose health they could seriously compromise. People they could kill, in fact. It might be around this risk, as much as a more generic threat to grandmother, that one might get a younger generation feeling they had more stake in the outcome.

Alas, it is not only young people who are paying insufficient attention to the risks posed by younger Australians to the health of the entire population. Equally problematic are many of the members of public health committees advising government, the ministers who are relying on their advice, and, frankly, not a few of the medical practitioners already up to their armpits in acute cases who wonder whether we can afford the luxury, the time, or the resources to investigate the presence of mild or asymptomatic cases in the general population. Or, for that matter, establishing who does not have the condition at all.

Members of the health committees and ministers will piously assure everyone that Australia is doing more mass testing, or more mass testing per capita, than almost anyone else. They have the figures to prove the number of tests, and, unlike figures pulled out of a hat by Donald Trump, these figures are not made up.

But even if we are doing more tests, we are not mass testing at all. Our tests are rationed. We are only bothering to test people we think will turn up positive. This might once have been justified, up to a point, when there was a shortage of tests available. That is not now the problem: the issue is the resource cost of extended testing - of testing everyone, perhaps regularly. It is said to be a low priority, or a distraction, as our focus shifts to increasing intensive care beds, training more health workers and developing extra hospital space.

In recent days we have slightly widened the testing net - and now also maintain a necessary watch on health practitioners working with acute cases who might have caught the virus. Testing of suspects is justified in its own right. Doctors with critically ill patients can sometimes push patients into the COVID-19 treatment stream before testing has established that their condition is COVID-19. But since coronavirus is far from the only source of respiratory crisis, it will probably be grudgingly, until COVID-19 is demonstrated by serology (proof of an antigen response to coronavirus by the person's body) or of strands of the coronavirus genome.

But using tests to stream patients is not a substitute for research into the spread of the virus into the population. And until we understand that epidemiology, particularly before we get a vaccine, we are doomed to have to slay the hydra over and over again as fresh victims emerge.

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Most of those presenting for the present tests will be turned away unless they "qualify" by way of travel or known exposure, and have serious symptoms. Even if there is good ground for suspecting exposure, but no evidence of any acute illness, the person will generally be told to go home and avoid contact with others for at least a fortnight. She or he may be put on a quarantine list - with compliance monitored by random checks - but most likely will be in the same sort of isolation as most other Australians. They are, after all, not ill. The health system has its hands full with those who are - and its problems will, in the short term, only get worse.

If mild cases are not going to be treated, some say, why bother to test them at all? Our collective efforts have to be focused on "smoothing the hump" of acute cases requiring treatment and threatening to overwhelm the available facilities, the equipment and the specialist staff able to help them. If we do not smooth that hump, after all, doctors will be forced to make choices about who gets treatment and who must be, in effect, written off. Will the criteria be age? Or having Alzheimer's? Or being immobile? Past credits, or future potential? These are not exactly novel choices for doctors working in acute care, on a battlefield or in a refugee camp. They are choices already being made as COVID-19 spiralled out of control in Italy, Spain the United Kingdom, Iran and, presumably, in China when the virus first appeared as a novel form of flu.

When doctors are rationing life and death here, we will all think that the Australian public health system has failed. And failed us. Some of those who felt that their relatives - old or young - received less than optimal care will blame the system, and the politicians. They will, we hope, not blame the actual health practitioners at the front line, because they will know that these people faced impossible choices and were working extended hours heroically, at considerable personal risk to themselves.

If only a very small proportion of those under the age of 50 are going to require hospital treatment, should we be diverting resources to finding out who has a mild or symptomless case (and who doesn't)? Shouldn't our efforts be focused on saving the lives of those who are at the greatest risk? That line of thinking has led some people, including a vice-chancellor-cum-health-economist writing in The Conversation this week, to say that mass surveys of the population are not best value for money. Not a priority. Much the same has been said by many doctors in the European Union (and Britain) after the World Health Organisation, two weeks ago, called for mass surveys.

There are front-line doctors who think like that too. They are focused on the patients they have, most with life-threatening illness. They don't have the time, they think, to worry about people without acute symptoms.

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Most Australians are perfectly healthy. They present themselves to doctors when they feel ill. Doctors are used to the patients coming to them. They assume that with most conditions, the sum of presentations to the health system is a fair average sample of the prevalence and incidence of a disease in the general population.

Yet we know that with an array of conditions, whole classes of Australians are ignorant, ashamed, or otherwise reluctant to seek medical advice. Younger less educated men, for example, are notorious for seeing the doctor only after acute trauma, such as a car accident. Probably half of the cases of type 2 Diabetes are undiagnosed. Some conditions widely prevalent in the community - sexually transmitted disease, for example - can be controlled only by vigorous case-finding and a degree of legal coercion. Over the past 50 years, Indigenous Australians have devised community-controlled medical services to deal with physical and cultural problems that have historically reduced Aboriginal access to health care.

About 43 years ago, Fred Hollows was leading teams going out into communities and conducting mass surveys for eye disease, including trachoma and cataract. The team came on one occasion to a town regularly visited by an ophthalmologist who held clinics at the hospital. He told Fred, proudly, he would see no blind people in this community. The team found 16. They found them because they did not wait for people to present, but used people in the community to bring in people needing help. People lost to the system even in a case where a public-spirited volunteer was available, but not hooked in.

The trouble with ignoring the need for epidemiological research, or denying its priority, is that the reservoir of the virus in the community is now among the groups who are asymptomatic or having only mild conditions. It is growing. And we have almost no idea who they are. We can no longer guess at who they are with questions about overseas travel, or physical closeness to a known victim.

Most of our future acute cases, more and more every week, are going to come from this reservoir in the general population - not from airports or boat terminals. The carriers will not be deliberately shedding and spreading the virus - most, indeed, will have no idea that they carry it. From what we know - and we know too damn little - a virus from an asymptomatic case can pass through several transmissions to further mild cases before catching a very vulnerable person who will die in agony. A mild or asymptomatic case is as much a risk to the community as a florid, severe case.

The reason we know too damn little is the lack of good research into the population dynamics of the virus and the conditions it causes. We have studied the course of the disease, or its aetiology, in any number of particular serious cases. By now we have a fairly good idea of the best treatments pending the development of a vaccine.

But we have very little idea of how the disease is transmitted from person to person, about the incidence and prevalence of the virus (as opposed to mild or serious cases) in the general population, and how that risk can be contained or countered.

When we have such knowledge, we can plan more effective strategies and tactics to reduce incidence and prevalence, and, possibly, its virulence and rate of spread through the community. A few other countries - South Korea and Singapore - have started some studies, but these have tended to work out of infected groups into the broader community, rather than from the community into those at risk.

We need such studies too, because sooner or later the incidence of the condition will decline, even before we develop a vaccine. We will breath sighs of relief, and reduce precautions. But there will still be many in the community who have not had the virus and have no resistance to it. There will still be people carrying the virus. A second outbreak a month or two after we have declared victory is perfectly possible. If we drop the ball, we could have another epidemic among the still susceptible, and further periods of lockdown. We can't have a plan to cope with coronavirus or COVID-19 until we know all there is to know about it.

Australia could pioneer systemic understanding of COVID-19 for the whole world. But it is justification enough that we need it for our own response to the condition. We have to pay a lot more attention to the pattern of prevalence in the population, even, or especially, among those who think they have little to fear.

At least until government began enforcing bans on gatherings, and being in public, our young people posed the greatest risk to the health of the population, including of themselves. But it's the failure of public health authorities to research and appreciate the who and how of virus-spreading, rather than the behaviour of young people, that is now becoming the most serious threat to public health. Scott Morrison has shown a commendable willingness to spend any amount of money to defend our health. There is no economy in saving money here.