NewsResearchers warn: 'Never take a negative result as a...

Researchers warn: 'Never take a negative result as a free pass'

Researchers warn against interpreting negative rapid test results as a free ticket. A study shows that hardly any test detects the omicron variant.

Munich – Many common Corona* rapid tests often do not detect an omicron infection. Researchers led by the Munich virologist Oliver Keppler from the Ludwig-Maximilians-Universität examined the performance of nine commercially available rapid antigen tests for detecting an infection with the omicron or the delta variant – and draw a sobering conclusion: Eight of the Paul Tests already tested by the Ehrlich Institute for earlier variants of the virus were worse at detecting omicron infection than delta infection, the study found, which was published in the journal Medical Microbiology and Immunology.

Researcher warns: Take precautionary measures even if the rapid test result is negative

“You should never take a negative result as a free ticket,” warned Keppler, who had already drawn attention to the topic in BR. * Especially in the omicron wave, precautionary measures such as keeping your distance and wearing masks are important to protect others and yourself protect. American researchers have examined the extent to which an infection protects against the virus. * Testing people without symptoms creates a false sense of security, especially in the current wave, Keppler warned. “In my view, asymptomatic testing with self-tests makes little sense,” said Keppler. However, it makes sense to test with good antigen rapid tests in addition to limiting contacts in the event of symptoms. Then the viral load is usually higher; Tests are more likely to work.

The experts demand: provide a list of reliable rapid tests

Like the Federal Minister of Health, Keppler is demanding that a short list of tests that are well suited for detecting omicrons be published quickly – after all, there are now 580 rapid tests on the market. “The one-eyed blind tests for the detection of omicron must now be quickly identified and published by the Paul Ehrlich Institute.” About ten readily available tests would be sufficient for this.

Between the end of October 2021 and the third week of January this year, the scientists examined 166 corona cases that had been characterized by means of PCR and sequencing, of which 101 were omicron infections and 65 were delta infections. Eight of the nine tests examined were listed by the Federal Institute for Drugs and Medical Devices as CE-marked antigen tests and also met the required minimum criteria, at least based on manufacturer information.

Pros and cons: No false positive rapid tests, but low test sensitivity

The first tests showed a positive partial result: at least there were no false positive test results, said Keppler. For this purpose, 115 swabs with a negative PCR test were examined. However, there were problems with the sensitivity of the test: with a very high omicron viral load (with a Ct value of less than 25), the rapid tests only worked in 31 to around 78 percent of the swab samples. With a medium viral load (with Ct values between 25 and 30), the hit rate for omicron infections was only zero to a good eight percent. Almost all tests detected more than 70 percent of delta infections when the viral load was very high. With a medium viral load, however, the hit rate was only 0 to 28 percent.

Influence on rapid test result: High viral load necessary for Omicron

In order to achieve a 95 percent detection probability, the viral load in a smear with Omicron had to be up to a hundred times higher than with Delta in some of the tests examined. “Overall, there is enormous heterogeneity in the rapid antigen tests for detecting omicrons,” said Keppler. “On the one hand, this must be clearly communicated and, on the other hand, a list of useful tests must be published quickly.” And which vaccine offers the best protection? (dpa) * and are offered by IPPEN.MEDIA.

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