ANALYSIS

Coronavirus: Could an instant COVID test become a reality?

Is a reliable, instant COVID test a possibility? Picture: Dion Georgopoulos

Is a reliable, instant COVID test a possibility? Picture: Dion Georgopoulos

In the absence of a vaccine, we have to learn to live with COVID-19.

One way of coming to terms with it more easily would be to have rapid, reliable and cheap tests available - what is sometimes called "a lab on a swab".

If airlines, for example, could test passengers in the terminal before boarding, there would be no (or little) risk of the virus travelling with infected passengers.

Sports venues and other gatherings could also have tests.

Rapid testing would be a way of living more easily with the virus while keeping the economy going.

So why not?

The short answer is that there are such tests available but they aren't quite accurate enough.

They are known as "antigen tests" and they have great advantages, according to Science, the magazine of the American Association for the Advancement of Science.

"Antigen tests are typically cheap, return results in minutes, and, like the (laboratory-based) genetic tests, reveal an active infection," the journal reported.

"They already exist for strep throat, influenza, tuberculosis, HIV, and other infectious diseases."

They are also cheap and easy to scale up into manufacturing large quantities.

But they aren't utterly reliable. On some calculations, half the negative results are false.

"Most antigen tests have a sensitivity of anywhere between 50 per cent and 90 per cent," according to Science.

"In other words, one in two infected people might incorrectly be told they don't have the virus."

Earlier in the year, the Spanish health authorities returned thousands of such tests to a Chinese firm after finding that they correctly identified infected people only 30 per cent of the time, according to the Spanish newspaper El Pais.

But isn't some risk of incorrect results acceptable?

The question is how much risk.

Epidemiologist Professor Adrian Esterman of the University of South Australia told ACM that the quick test was very good at telling people they aren't infected but not so reliable at detecting infections in those who have it - and that's the measure which counts.

"At the lowest end, one in two infected people might be told that they do not have the disease," he said.

Until these fast tests can made more sensitive, "it is unlikely that they will be widely used".

But a debate continues. Some doctors say that a relatively less reliable test is still worth using if it gives quick - immediate - results.

People could be tested many times so infected people missed first time round could be detected second or third time.

And the big advantage is the speed. Waiting two days for a laboratory result means two days when an infected person remains undetected.

So what's the alternative?

The more reliable test is known as an RT-PCR test (Reverse transcriptase Polymerase Chain Reaction).

The common view of the medical authorities is that this remains the best way because of its reliability.

The testing and analysing apparatus is being made more mobile so the time between testing and laboratory analysis can be cut.

But there's a snag with this, too. "These systems can provide quicker results, but cannot do as many tests at once," according to the Department of Health.

Is technology the only constraint?

Skilled workers to administer tests and analyse results are in short supply in some poor countries.

But there is a race on develop new ways of testing. It's a commercial race but also one that is important for stopping and slowing the disease.

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If there are different types of tests, medical staff could use a mix of methods where different instruments and materials are available.

Researchers are also building up knowledge which may be useful for other viruses, yet unknown.

Whatever happened to herd immunity?

At the beginning of the epidemic, there was an idea that allowing infection to happen would build up immunity in the community - "herd immunity".

But the science has now advanced to discount the idea.

Two Swiss scientists have concluded that immunity is "incomplete and temporary, lasting only several months to a few years".

"At what appears to be the tail end of the first wave of the pandemic in Switzerland, about one in 10 people have developed detectable antibodies against SARS-CoV-2, despite the fact that it was one of the more heavily affected areas in Europe," the researchers wrote in The Lancet.

A separate study with more that 61,000 participants in Spain found that only five per cent were immune from COVID-19, including people who had already had it.

"The results are particularly concerning as Spain was one of the hardest-hit COVID-19 countries, with over 28,000 recorded deaths," according toLaboratory Equipment magazine. The studies raise a disturbing possibility: this thing won't go away. Even catching it doesn't give automatic immunity.

"In light of these findings, any proposed approach to achieve herd immunity through natural infection is not only highly unethical, but also unachievable," Swiss researchers Isabelle Eckerle and Benjamin Meyer said.

So where next?

Keep keeping your distance. Keep washing your hands. Keep hoping for a vaccine.

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This story Why not have an instant COVID test? first appeared on The Canberra Times.

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