For the holidays: why you shouldn’t trust an antigen test

Christmas holidays with family reunions imminent and many who want to be on the safe side are already planning when and where they can best be tested. For many, express tests, which they can do themselves at home just before the festival, are an obvious option. Belgian researchers are now warning against relying on antigen tests.

They examined how well antigen tests were in people who tested positive for infection and high concentrations of virus in the air they breathe. The result: in the first two days of infection, the concentration of virus in the breath was high, which means that the people were infectious to their surroundings. Most of the antigen tests were negative.

PCR tests are more reliable

According to researchers, rapid tests do not work in the first few days of infection, as one study showed. It is different with PCR tests: they also provide reliable results in the early stage of infection.

“A negative rapid antigen test shortly before a meeting does not guarantee that others will be protected, especially if the person being tested has recently been exposed to the virus,” said study author Emmanuel Andre, a microbiologist at KU Leuven.

It was surprising for the researchers to find high concentrations of the virus in the breath even at the beginning of the infection. This is an indication that the virus can be transmitted very early in the case of infection. “A negative antigen test should not replace self-isolation when the potential for disease is high, such as during the first seven days after exposure to a high risk,” Andre said.

Nasenabstrich

In their study, the researchers examined 58 people who had been in direct contact with infected people and tested them regularly with different tests over a two-week period. Of the 58 people, eleven later developed Covid-19. However, in the first two days of her infection, antigen tests failed to detect half of the infections. On the other hand, polymerase chain reaction (PCR) tests obtained using nasal swabs have reliably demonstrated the disease.

What’s called Aerosol tests, a type of polymerase chain reaction (PCR) test in which breath is collected and tested on a special silicone slide, showed high concentrations of virus in the breath on the first day after infection.

The study has been published as an introduction to print here can be read.