Nasal swabs, PCRs, rapid antigen tests… with so many different diagnostic tools at our disposal, what will COVID tests look like in the future?
A new study from the New Zealand Medical Association (NZMA), published in the New Zealand Medical Journal, found that rapid PCR (polymerase chain reaction) may be an accurate and fast diagnostic tool for COVID testing in regional areas.
But rapid PCR is just one of three different types of COVID tests available in Australia and New Zealand. What is the difference between them, and which ones might we be using in the future?
Nucleic acid tests (PCR)
These tests are used to detect specific nucleic acids – the molecules that make up DNA and RNA – that are unique to SARS-CoV-2.
The most common nucleic acid test is the PCR test, which is considered the gold standard of COVID diagnostics. It’s very accurate and specific to the virus.
One type of PCR test is the reverse transcriptase (RT) PCR test, which specifically searches for viral RNA in a nose and/or throat swab. Results usually take a few hours, but many swabs can be tested at once, making them a convenient choice for mass testing.
They do, however, require special equipment in a laboratory, and trained technicians to conduct and analyse them, so they aren’t a test that can be conducted at home.
“They require complicated analytic equipment only found in pathology laboratories, and need expert lab technicians to run the equipment,” says Professor Adrian Esterman, Chair of Biostatistics at the University of South Australia. “Each PCR test takes about six hours to run, so it is not surprising that tests are returned usually after 24 hours.”
Rapid PCR tests use a type of PCR that only takes 20 minutes. They are portable and small and so can be conducted outside of a laboratory, which may be especially useful for regional areas without diagnostic laboratories.
However, they can only test one sample at a time, which means they work best when there is a low volume of people needing a test.
Rapid antigen tests
In Australia, rapid antigen tests are used by trained medical professionals to determine whether a symptomatic patient has COVID. They require a nasal or throat swab to test for the presence of known viral proteins on the surface of the virus.
This involves mixing the swab with a solution that breaks the virus open, releasing proteins. On a paper strip, these proteins bind to special antibodies that change colour when the protein is present – like an at-home pregnancy test.
They can provide a result within 15 to 30 minutes, but they are considered less sensitive than PCR tests – meaning they aren’t quite as good at recognising tiny amounts of the virus. For this reason, they are more effective when used in the early stages of infection – usually within five to seven days of symptoms beginning – when viral load is the highest.
A positive rapid antigen test is generally considered accurate, but if somebody who has symptoms returns a negative test, they will usually have a follow-up PCR test just to make sure.
Because of this, rapid antigen testing is generally discouraged for home use – positive cases may sometimes be missed due to a false-negative result.
However, rapid antigen testing is much cheaper and quicker than PCR, and doesn’t require special equipment.
Serology antibody testing
Because COVID-19 swept the nation so quickly, serology antibody tests received expedited assessment so that they could be available as soon as possible.
These tests require special laboratory equipment and trained professionals to take a small finger-prick blood sample. This is placed on a test strip to detect one of two specific antibodies in the blood – immunoglobulin G (IgG) and immunoglobulin M (IgM) – that the immune system produces when infected.
Like the rapid antigen test, this looks like a pregnancy test and takes 15 to 30 minutes to produce results.
The benefits of this test are that it shows any past exposure a person has had to SARS-CoV-2, and it is quick.
But there are a few downsides.
First, the immune system doesn’t start producing antibodies immediately after infection, so it could be up to two weeks after exposure before the serology antibody tests are effective. This is a long time, considering COVID’s infectiousness.
Secondly, IgG and IgM are also produced when a person is ill from other viruses, so the test doesn’t necessarily show whether the antibodies were produced in response to SARS-CoV-2 or other common coronaviruses, which may lead to false positives.
Lastly, these tests don’t show the quantity of virus present, which PCR and antigen testing can do to some extent, and so don’t convey information about whether somebody might still be infectious.
What will COVID tests look like in the future?
It will probably look a little different to each person, depending on where they live.
“Like most predictions for COVID-19 the future of COVID-19 testing is still rather nebulous with regards to which way this will head,” says Dr Roger Lord, a medical scientist from the Australian Catholic University.
“The picture becomes even more confusing once international boarders open and travel commences between Australia and countries where the rate of vaccination against COVID-19 is low.
The virus has a greater ability to mutate in populations where vaccination rates are low – for example, South Africa. Infected individuals with a new variant of COVID-19 returning to Australia may in turn compromise our current vaccination strategy.”
Currently, self-tests for COVID-19 are prohibited in Australia, and purchase and import of COVID tests are banned for people in New Zealand, except in the case of people, businesses and point-of-care facilities (such as doctors and hospitals) authorised by the Director-General of Health.
This is primarily because reading and understanding COVID tests is considered complex and best done by a trained professional. However, these tests are now readily available for everyone in the UK.
Looking ahead, we may most noticeably see a change in which tests are the most common. For example, PCR tests are more expensive than rapid antigen tests, so the latter may become more prevalent, especially when vaccination rates are high.
“When we have high vaccination rates, we will not be willing to spend millions and millions of dollars on PCR,” Dr Ian Norton, a specialist emergency physician at Respond Global, has previously told Cosmos. “Instead, we should be doing a light, rapid test for catching those one or two people who have broken through their vaccine and are now infectious.
“Rapid tests are very effective at picking up super spreaders. This is where they are most useful.”
We can also learn from what other countries have done.
“We know that other countries are opening borders for the vaccinated and using a number of strategies among their population to learn to live with the virus in a cautious and informed way,” says Jaya Dantas, Professor of International Health in the School of Population Health at Curtin University
“Antigen tests are easy to use and are currently being used in the USA, UK, Singapore and many European countries. Due to their quick turnaround testing times, they can play a part with truck drivers, sports people, teachers, travellers and the general population just wanting to know their COVID-19 status.”
Some large companies – such as airports and food manufacturers – in New Zealand have recieved rapid antigen tests to rollout in the workplace part of a trial to expand COVID surviellence. These tests may become standard requirements in business places.
We may even see rapid antigen tests commonly used to screen people at big events or places where large volumes of people are unavoidable.
“Rapid antigen tests are ideal for airports, transport hubs, industry settings, schools etc,” says Esterman. “Their slightly poorer accuracy is less important in these situations.
“They are not widely available in Australia, yet a popular one used in the USA is made in Queensland.”
Rapid PCR tests might become more common in regional places, because they are cost-effective and small. With lower numbers of regional residents, the single-sample device may not be a hindrance.
If hospitalisation rates drop, we may even find that one day most tests are conducted through a GP, much like how we monitor flu.
Whatever the future brings, COVID tests will, without a doubt, be a part of it.
Deborah Devis is a science journalist at Cosmos. She has a Bachelor of Liberal Arts and Science (Honours) in biology and philosophy from the University of Sydney, and a PhD in plant molecular genetics from the University of Adelaide.
Read science facts, not fiction...
There’s never been a more important time to explain the facts, cherish evidence-based knowledge and to showcase the latest scientific, technological and engineering breakthroughs. Cosmos is published by The Royal Institution of Australia, a charity dedicated to connecting people with the world of science. Financial contributions, however big or small, help us provide access to trusted science information at a time when the world needs it most. Please support us by making a donation or purchasing a subscription today.