Health Analysis

Rapid testing and viral mapping can help beat COVID-19

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Rapid antigen tests are highly effective in detecting the virus (Screenshot via YouTube)

More testing and better knowledge of how the COVID-19 virus works are crucial in defeating its spread, writes Dr Kim Sawyer.

WE CAN’T DO a road trip without a GPS. We can’t fly a plane without radar and we can’t fight a virus without knowing where it is. We never mapped the virus. We have been flying blind.

COVID-19 is more powerful than other viruses because it hides better. The asymptomatic are driving the virus. The power of the asymptomatic spreader was evident from the beginning. A 20-year-old woman living in Wuhan travelled to Anyang. She met five relatives, four of whom became symptomatic. However, the young woman remained asymptomatic and tested positive only once in four tests. The virus hides so well that even the tests cannot detect it.

Countries that conducted extensive antibody testing showed the prevalence of the virus. Even in the first half of last year, antibody studies in New York showed 15% of the population had been exposed to the virus. It was the same in London, New Delhi, Moscow and Iceland. The story was the same wherever extensive antibody testing was conducted.

The only extensive seroprevalence study conducted in Australia by researchers at ANU in July last year suggested more than seven times as many had been infected as the tests were showing. That was before the Melbourne outbreak. Zero-COVID was never a tenable assumption. The virus hides too well.

We needed to test across the population. We needed to find spreaders before they spread, to sample the virus as we do with voting, to sample the young and the mobile. As any statistician knows, you do not get people to select themselves. You select them. The asymptomatic were never tested. It was the biggest mistake of 2020. We never mapped the virus.

We are making the same mistake now. We need not only mass vaccinations but also mass testing for two reasons. Vaccination protects a person from getting infected and infecting others. However, there will always be breakthrough infections, the vaccinated who contract the virus. Vaccines prevent serious illness but not necessarily infection.

A recent study in the New England Journal of Medicine found two doses of the Pfizer vaccine were 93.7% effective against the Alpha variant of COVID-19 and 88% effective against the Delta variant. Two doses of AstraZeneca were 74.5% effective against Alpha and 67% against Delta. The incidence of breakthrough infections is small but still present. In the United States of 164 million people fully inoculated against COVID-19, there have been 7,101 hospitalisations and 1,507 deaths due to breakthrough infections. The vaccinated must still be tested.

The second reason for mass testing is the viral load. The viral load matters. Those who are seriously ill have viral loads as much as 60 times those with mild symptoms. Super spreaders are those with high viral loads. A Colorado study found that only 2% of the infected carry 90% of the viral load. The Delta variant is distinguished by a high viral load — in one Chinese study, as much as 1,000 times higher than other variants. We must mass test to track the viral load.

The good news is that rapid tests make mass testing possible. Slovakia recently tested all its 3.6 million population with rapid tests. Wuhan is mass testing 11 million people. Rapid antigen tests are being used in the U.S. after being approved by the CDC in April.

Antigen tests are immunoassays that detect a current viral infection and have three advantages. They are point-of-care tests that can be conducted at home, a pharmacy or a clinic. They take 30 seconds, produce a result in 15-30 minutes and can be conducted three times a week. This is important because with multiple testing, the probability of error gets close to zero.

Rapid antigen tests cost $10 compared to $150 for a PCR test. They can be produced in the numbers necessary for mass testing. In the UK, lateral antigen tests are used to pre-screen COVID-19 infections and confirmed by a PCR test. An Oxford University study showed this increased the probability of detection to near certainty. We must do the same. The Therapeutic Goods Administration has approved 130 types of rapid antigen tests. They are now used in approved workplaces including construction. We must extend rapid testing further. 

Let’s map the virus using rapid tests and stop flying blind.

Dr Kim Sawyer is a senior fellow in the School of Historical and Philosophical Studies at the University of Melbourne.

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