Fight against Corona: How well do rapid tests detect the Omikron

While the rapid tests continue to play an important role in the fight against the pandemic, there is increasing evidence that they work worse with Omicron than with other variants of the corona virus.

Researchers from Munich provide the latest indication of this in the magazine "Medical Microbiology and Immunology".

The researchers examined nine commercially available rapid tests.

All but one had worse hit rates on samples from omicron patients than on people infected with the delta variant.

While eight tests recognized the delta variant in well over 70 percent of cases with high virus levels, only two managed to do so at Omikron.

Three tests did not even work for every second Omicron infected person.

In plain language, this could mean: Every second person infected with Omikron gets a negative result in the tests concerned - and thus the green light to enter old people's homes and clinics or to visit relatives at risk.

Particularly explosive: Eight of the tests examined had previously been tested by the Paul Ehrlich Institute (PEI) and found to be good, but with other variants of the virus.

One of the study authors, the virologist Oliver Keppler from the Ludwig-Maximilians-University Munich, said in view of the results and the fact that more than 99 percent of the infections in Germany are omicron: “You should never take a negative result as a free ticket take.” He also warned that testing people without symptoms creates a false sense of security.

Nevertheless, the national test strategy currently still provides for preventive examinations of school children, for example, with the rapid tests.

Big problem or small weakness?

It is quite plausible that the tests on Omicron react differently than on Delta.

Because the latest variant has mutations in the nucleoprotein, the component of the virus that the tests are designed to detect.

Still, it's unclear whether this is a major issue that challenges the usefulness of the tests, or just a minor weakness.

On the one hand, this is due to the limitations of the most recent work from Munich and, on the other hand, to an overall confusing study situation.

In recent months, several research groups have examined the sensitivity of the tests at Omikron.

Results from Switzerland published in advance in January point in the same direction as those from Munich.

Scientists there tested seven rapid tests, four of which detected Omicron significantly worse than Delta.

Researchers from the United States looked at three tests and found almost no drop in Omicron's hit rate.

Another group from the United States even found that a test at Omicron was slightly more sensitive than Delta.

In their study, scientists from Australia hardly noticed any differences between delta and omicron in ten tests.

However, all of these studies have the limitation that the samples did not come directly from the nose or throat of the patient.

These were preserved swabs.

The ones from the Munich investigation were collected between October and January and stored in a “liquid transport medium”.

The researchers stored some of them, but not all, at minus 20 degrees.

This procedure is quite common.

The PEI also does not use fresh samples in its assessment of the tests - anything else would be difficult to do logistically.

It is possible that this will affect the results of the tests.

In addition, it was unclear in the Munich study whether the infected had been vaccinated or had recovered.

This can also affect the test results.

Large differences between the tests

Real-life observational studies provide results that are suitable for everyday use, but leave other questions unanswered.

In the United States, medical professionals have identified 29 cases of omicrons in people tested daily in the workplace.

For 28 of them, the rapid tests showed a negative result, although the people had virus levels that can be quite contagious.

This is how the scientists interpret their results, which have not yet been reviewed.

Four of the people observed are said to have even infected others, although their quick tests were negative.

However, since the researchers focused on omicron in this study, it is unclear whether the problem with this variant has actually gotten bigger or whether only the known weaknesses are coming to light.

However, one finding from most studies is that there are major differences between the rapid tests.

If you want the most reliable result possible, you should use a test that is particularly popular with Omikron.

Federal Health Minister Karl Lauterbach (SPD) announced at the beginning of January that the PEI would draw up a list of such tests.

According to the institute, it will be available at the end of February at the earliest.

There is already a small insight into the results: according to reports, the Bundeswehr Institute for Microbiology evaluated 28 tests for the PEI;

four of them would have done worse with Omikron than with the other variants.

In general, the question of the quality of the tests in Germany is largely open - Omikron or not.

The PEI independently checked the sensitivity of only 321 of 600 common rapid tests and 43 of 61 self-tests on the market.

For the rest, trust the information provided by the manufacturer.

That should actually change in May, when a new regulation of the European Union comes into force.

But because the laboratories are not ready yet, the transition phase has been extended – until 2025.