Will the test strategy come under pressure? Antigen test turns out not to be as effective as thought shortly after Covid infection

The result of a rapid antigen test appears to be less reliable than expected during the first two days after an infection with Covid-19. This is reported by scientists from KU Leuven, UZ Leuven and technology company imec. They conducted a study with never-before-used molecular tests on aerosols.

This shows that the exhaled viral amount (the alleged measure of infectiousness) peaks before the rapid antigen test is really reliable. In short: people can already transmit the virus shortly after being infected, while the rapid test still indicates ‘negative’.

Consequences

That does come with consequences. So is the rapid antigen test has become an additional tool to fight the pandemic, and has also been seen as a full-fledged test by policymakers. It result of a rapid test has meanwhile also been recognized to board the plane or attend events. The test is almost on par with the PCR test in terms of efficiency. Only this turns out not to be true.

A specially designed sampler from imec was used for the study, which can detect the number of SARS-Cov-2 in exhaled air. The test included 58 high-risk contacts, 11 of whom developed an infection. All subjects were monitored daily for two weeks, with nasal, saliva, breath and antigen testing.

• During the first two days of infection, half of the rapid antigen tests resulted in false negatives.
• The PCR tests, performed on the nasal swabs, showed a lower viral load in these first two days.
• PCR tests performed on the breath samples showed a high viral load.
• A high viral load was also measured during exhalation. This is a first indication that the virus is easily transmitted during the first two days after being infected.

Consultation committee and Christmas

The question everyone is probably asking right now: what about Christmas? Experts and politicians have been calling for a quick test for weeks before you visit friends or family. “That’s the only way you can be sure”, was suggested. Unfortunately. A new Consultation Committee is on the agenda for Thursday between the GEMS advisory group, the federal Core and the Prime Ministers of the federal states.

It is expected that this study will also be discussed in detail there, and that it may ultimately contribute to tightening up. Although all figures are going in the right direction, tightening up seems to be the only option, virologist Marc Van Ranst and federal Minister of Health Frank Vandenbroucke (Vooruit) have already pointed out.

(lp)

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