Frankfurt The coronavirus variant called Omikron, sequenced for the first time in South Africa, could limit the effectiveness of the previously approved Sars-CoV-2 vaccines due to the large number of mutations in the so-called spike protein. Experts fear that. In addition, a second question arises: Do the currently available corona rapid tests even reliably detect the Omikron variant?
Currently available rapid antigen tests can detect an infection, but not explicitly whether it is also an omicron variant. For this purpose, so-called genome sequencing of the virus is currently necessary. Fears that corona infections caused by Omikron can no longer be detected at all because of the mutations in the virus have not yet been confirmed.
The currently predominantly used rapid antigen tests also show a positive result with Omikron. Virologist Sandra Ciesek illustrated this in a tweet earlier this week. Afterwards, both a nasal and a throat swab were carried out using the tests from the manufacturers Roche, Siemens and Flowflex. According to Ciesek, the tests were all positive.
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The omicron variant B.1.1.529 mainly shows numerous mutations in the so-called spike protein. With the help of this protein, the virus can penetrate human cells and multiply there. The existing vaccines address this mechanism. Rapid antigen tests, however, are not.
According to private lecturer Roman Wölfel, senior physician and head of the Bundeswehr Institute for Microbiology in Munich, most rapid tests identify the virus via its nucleocapsid protein. The Omikron variant does not show any mutations that would lead to an impairment of the function of rapid antigen tests, according to Wölfel.
Abbott and Siemens Healthineers announced that they had performed evaluations of their rapid antigen tests. They showed that these tests could also reliably detect infections caused by the Omikron variant. The Swiss pharmaceutical company Roche also commented accordingly. According to Siemens Healthineers, the inquiries about the tests are still at a high level. The main buyers are still the federal, state and local governments and meanwhile also industrial customers with large productions.
In addition, Healthineers offers its rapid tests via a web shop. The manufacturer Abbott states that the company can ensure reliable delivery to pharmacies in Germany. The company has manufactured more than a billion Covid-19 tests since the pandemic began.
How do you recognize the quality of a rapid test?
Regardless of the virus variant, with antigen rapid tests, the detectability of Sars-CoV-2 is always worse compared to PCR tests in the laboratory. Rapid tests, regardless of whether they are carried out professionally or on their own, detect certain proteins from the virus envelope, the so-called antigens, in the secretions of the respiratory tract.
This does not always work reliably, for example when the sample contains few viruses, as is the case at the beginning or at the end of an infection. The standard PCR laboratory test looks for genetic material of the virus and also detects small amounts. Since a positive result in the antigen test can also be false, a PCR test should always follow in order to reliably determine an infection.
The Paul Ehrlich Institute (PEI) published a study at the beginning of November that showed that the sensitivity of rapid antigen tests for personal use varies greatly overall. To this end, the PEI and other institutions examined a total of 122 Covid-19 antigen rapid tests.
Every fifth test failed because it did not achieve the required sensitivity of at least 75 percent: This means that the test must show a positive result in at least 75 percent of the cases if a certain amount of virus is present in the sample. A list of the examined tests that meet this criterion can be found on the website of the Federal Institute for Drugs and Medical Devices.
When does the use of rapid tests make sense?
Antigen tests can be useful in the event of symptoms to clarify suspicions of Covid-19. However, scientists agree that they don’t work as well in people who don’t have symptoms. People with negative test results can still be infected. And since a positive result in the antigen test can also be false, a PCR test should always follow in this case in order to reliably determine an infection.
Virologists are confident that the Omikron variant can also be detected using the so-called PCR tests in the laboratory. “The gene segments of the virus that are used for PCR diagnostics are hardly or not at all changed in B.1.1.529. This new variant will be recognized just as reliably with PCR tests, ”says Oberstarzt Wölfel.
Danger from omicron mutation still unclear – hope for mild progression
Virologist Sandra Ciesek, Director of the Institute for Medical Virology at the University Hospital Frankfurt and Professor for Medical Virology at Goethe University, had already published the results of the first laboratory tests, which show that the Omikron variant can also be detected in certain target genes using PCR tests can. The test systems from the manufacturers Roche, Abbott and Genexpert were used.
“The PCR systems established in the laboratories also determine a corona infection caused by the Omicron virus,” confirmed Michael Müller, first chairman of the Accredited Laboratories in Medicine (ALM) on Tuesday. However, the variant itself must be identified by means of sequencing. That doesn’t happen regularly with all rehearsals. Every week, the specialist laboratories examine a representative sample of the first-time Sars-CoV-2-positive PCR samples with whole genome sequencing according to the specifications of the Robert Koch Institute. This is how Omikron was discovered in Germany.
“In addition, we will also examine samples for the mutations typical of Omikron if there is a specific suspicion of an infection with the corona variant,” added Müller. This can be the case in particular for travelers returning from the relevant regions and their contact persons.
Overall, the specialist laboratories have once again increased their PCR capacities – by two percent to 2.2 million tests per week. According to the ALM, this is sufficient, but there are regional overloads depending on the infection situation. A total of 1.84 million Sars-CoV-2 PCR tests were carried out in the past week, more than ever before in the pandemic.
More: Moderna boss thinks vaccines are less effective against Omikron.