Coronavirus: How long before a quick, reliable cheap test comes out?

Or: there may eventually be a vaccine but it is so far away, and the task of vaccinating the population of the globe is so big, that the prospect of a vaccine rescuing us all is distant.

If either of those gloomy propositions is true, we will have to learn to live with accursed COVID.

If that is so, testing - reliable, cheap, quick testing - will be the way forward.

It needs to be quick because there's no point in testing and then waiting for days for a result. Airlines, train and bus companies, as well as concert venues or colleges need to know immediately that a person is free of the virus.

It needs to be cheap so it can be done many millions of times, and repeatedly: just because you haven't got the illness now doesn't mean you won't catch it tomorrow.

And it needs to be reliable. There is no point in a test which fails to detect a sizable proportion of infected people.

There are two types of test: one detects whether the virus is there in the body at the time of testing and the other tests whether the person has been infected in the past.

The first type is the one used all over Australia. A swab on a plastic "stick" is pushed up to the back of the nose and a sample taken. It's unpleasant but not painful.

It's called RT-PCR (reverse-transcriptase polymerase chain reaction. Don't ask). But the gist of it is that a chemical reaction on the sample reveals the presence of the virus in the body.

The drawback is that it's not completely reliable, according to Sotiris Vardoulakis, professor of global environmental health at the Australian National University.

For positive tests (where the person tested is found to have the virus), it gets it right in 90 per cent of cases.

For negative tests (where the test says the person is clear of the virus), it gets it right 70 per cent of the time.

In other words, if ten people who actually are infected with Covid-19 are tested, three of them on average are incorrectly told that they do not have the virus.

And Professor Vardoulakis says that the test, which involves laboratory analysis, is expensive.

This is the one to find out if people have had the disease in the past.

There are different tests but the principle is the same: the tester takes a blood sample with a small pin-prick and the blood is then analysed (you will have your own view but many might find this less uncomfortable than the plastic "stick" right up the nose).

The blood sample contains the antibodies which our bodies produce to fight viruses.

If the sample contains a lot of the coronavirus antibodies, the test indicates the virus has been there - that is, that the person has been infected.

One snag, according to Dr Larisa Labzin of the Institute for Molecular Bioscience at the University of Queensland, is that newly infected people might not have built up enough of these antibodies to be detected in the blood sample.

They may have the virus but it can't be detected yet. But a lot of research is going on around the world.

Any test must identify the coronavirus and only the coronavirus. "Think of it like trying to identify different types of fruit," Dr Labzin said.

"It's easy to distinguish between an apple and an orange. But determining whether we have an orange or a mandarin is much harder.

"Our test has to be sensitive to more than just colour, shape, and texture of the fruit's skin. We would need to look for a characteristic unique to the orange, such as the roundness of the orange, or how easy it is to peel the skin off."

But the advantage of these types of test is that they give a lot of very useful information.

"They are good at showing how many people have developed the disease so we know how much immunity there is in the community," Dr Labzin told this paper.

And it's easy to do. Dr Labzin likens them to pregnancy tests.

The advantage of knowing how many people have had the coronavirus is that the authorities would then know how much potential immunity there is in the community.

People who are immune are not a danger to anyone else. They can travel freely without being infected or infecting others.

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But scientists don't know how long immunity lasts. On top of that, the virus may mutate so immunity from one type may not mean immunity from the new, mutated type.

Testing would have to be repeated. Professor Vardoulakis said people who had already caught COVID-19 would have some immunity but it wouldn't be clear for how long.

Epidemiolgist Adrian Esterman, Professor of Biostatistics at the University of South Australia, told this paper that Britain is about to introduce a new, faster test to see if people have the coronavirus at the time of testing.

"The company that manufactures it, Oxford Nanopore Technologies, says that it has the potential to provide millions of tests a month.

No details have been released yet of its price or diagnostic accuracy, but reportedly, it has a sensitivity similar to existing RT-PCR tests. Sensitivity is the ability to correctly detect an infected case."

It seems not. A lot of progress is being made but none of the experts we talked to thought that reliable and cheap tests, with very quick on-the-spot results, was about to come on to the market.

"I certainly hope that by the end of the year, we will be closer," Dr Labzin said.

In other words, the game-changer test may take as long as the game-changer vaccine.

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