With the rapidly increasing incidences of omicrons and the 2-G-Plus rule in more and more areas such as the hospitality industry, rapid antigen tests have become more important than ever as a detection instrument, but at the same time their reliability is increasingly being questioned.

The Paul Ehrlich Institute has confirmed the announcement made by Federal Health Minister Karl Lauterbach on Sunday evening to carry out a separate review of the officially listed rapid tests.

Joachim Müller-Jung

Editor in the features section, responsible for the “Nature and Science” section.

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The background to this are the results of smaller studies, especially in the USA, according to which the rapid tests no longer reliably provided a correct result in the first few days after infection with the strongly mutated variant.

Are the rapid tests unsuitable in the current omicron wave, and would that mean more PCR tests would have to be carried out (and paid for)?

Three reasons and more why rapid testing is still useful:

1. Limited PCR capacities

Both Lauterbach's ministry and most virologists hold fast to the usefulness of rapid tests. This is not only due to the rapid tests themselves. According to a data analysis by the Accredited Laboratories in Medicine (ALM), the utilization of the PCR capacities of almost 2.3 million tests per week has risen sharply with the surge in Omikron infections. The positive rate of the samples sent is already more than 23 percent, which means that further bottlenecks can be expected in the next few weeks. PCR tests are the gold standard for virus detection, they very reliably identify the infected by detecting the genetic material of the virus.

The cheaper, but also much faster, rapid tests, on the other hand, determine whether someone is currently infectious by detecting fragments from the virus envelope - and only work when the amounts of viruses in the sample material are very high and the tested are very likely to be in the virus Moment are also contagious.

In the first two to three days after the infection and also after the peak of the virus replication in the nasopharynx, most of these tests do not work, you get a negative result - but most infected people are not yet or no longer highly infectious.

2. Tests do capture omicrons

Some studies before the Omikron wave, for example at the Charité in Berlin, had shown that the meaningfulness of the various antigen tests differed significantly from one another. Antigen tests are therefore questionable for reliable diagnoses, but as an instrument of public health protection they can help, especially with rapidly increasing incidences, to prevent massive amounts of infection from highly infectious people - provided those who test positive isolate themselves. Therefore, despite concerns about sensitivity, rapid test capacities are being expanded around the world. There are now increasing concerns about the multiple mutated Omicron variant. The replication cycle of this virus is different from previous variants. Because this has apparently reduced the time window for detecting high levels of virus in the nose and throat,the risk for infected and actually infectious people to get a wrong result has increased.

Virologists such as the Frankfurt clinician Sandra Ciesek or the Geneva virologist Isabelle Eckerle, who have already gained experience with Omikron detection, therefore recommend in public forums that at least two rapid tests be carried out at intervals (starting at the latest two to three days after an alleged contact) to use. This increases the probability of a correct test result. According to the urgent advice of the virologists, people with cold symptoms should stay at home for the time being and test themselves repeatedly, even if the quick test result is negative.

Basically, this is shown by current studies (as here in medRxiv) in which individual antigen tests were compared with PCR test results, the rapid test products at Omikron, which have already been classified as reliable, respond as well as with earlier virus variants.

One of the reasons for this is that the protein from the virus envelope, which is crucial for antigen detection, only contains two new mutations, which obviously do not significantly change the molecule.

3. Adjustments to the test procedure 

Individual studies, which have not yet been peer-reviewed, indicate that omicrons initially multiply quickly, especially in the oropharynx, and can therefore be detected a day earlier with throat swabs in the mouth than with nasal swabs alone (here and here).

4. Critical examination of previous tests

The Paul Ehrlich Institute now wants to present a positive list of rapid tests that work best with Omikron evidence in the next few weeks.

Of the 245 rapid antigen tests checked by mid-December, four out of five common products (before the Omikron wave) were able to reliably detect high virus concentrations.

From May 2022, only independently tested rapid tests should then be reimbursable and usable in test centers.