With results in a few minutes, why are we not yet switching to ‘game-changer’ saliva tests for Covid-19?

15 October 2020 By Paul Martin

The British Medical Journal has pointed out that there are huge advantages in using a rapid saliva test for Covid, even though they appear to be 20 per cent less accuracte in detecting the disease.

A very convincing American analysis has already shown its benefits, as correspondent.world previously reported.

Here’s what the BMJ wrote:

In September the World Health Organization approved two “lateral flow” antigen tests, which display a result like a pregnancy test, are small and portable, and deliver a result in just 15-30 minutes.6 Made by the South Korean company SD Biosensor and the US company Abbott, they are the first rapid tests to meet WHO’s specifications. An independent evaluation of the SD Biosensor test by the Foundation for Innovative New Diagnostics (FIND) found that it had a clinical specificity of 99.3% and a clinical sensitivity of 76.6%.7 No independent evaluation of the Abbott test is yet available.

Jon Deeks [professor of biostatistics at University of Birmingham] called these tests a “game changer” for low and middle income countries, where RT-PCR tests are not widely available, because they can be done without a laboratory, running water, or electricity.

Such benefits are attracting interest from higher income countries, too: Germany has already ordered 20 million of the tests, and France and Switzerland have also announced intentions to purchase.

It is not yet clear whether the UK will follow suit. Deeks says we need to assess carefully the benefits and the harms of using a more accessible and quicker but less accurate test.

The FIND study shows the Abbott and SD Biosensor tests to be about 20% less sensitive than PCR, Deeks told The BMJ. He says, “They miss cases with lower viral loads, as they don’t do the amplification stages like a PCR test. This means they may miss people who are at an early stage of infection and give them a false negative.

“This could give people false confidence that they are not infected, which would be a problem if people stopped social distancing—for example, if it was used to allow people to go into a football match.”