Antigen tests often fail to pick up Omicron, Munich researchers find

Researchers at Munich's Ludwig Maximilian University have found that antigen tests are often highly unreliable when it comes to detecting an infection with the Omicron variant.

Antigen tests often fail to pick up Omicron, Munich researchers find
An employee of the test center holds a corona rapid test in a corona test center in the Schiene festival hall in Saxony. Photo: dpa-Zentralbild | Sebastian Kahnert

To be 95 percent sure of picking up an Omicron infection, some of the accredited antigen tests needed a viral load up to a hundred times higher than with a Delta infection, the team led by virologist Oliver Keppler found.

A viral load is the amount of virus detectable in a patient’s body. 

Overall, eight of the nine commercially available antigen Schnelltests in the study didn’t pick up Omicron as well at the Delta variant, according results published in the journal Medical Microbiology and Immunology.

“There is tremendous heterogeneity in rapid antigen tests in terms of detecting Omicron,” Keppler said.

“On the one hand, this needs to be clearly communicated, and on the other hand, a list of usable tests needs to be published quickly,” he said.

The scientists looked at 166 cases of infection between October and January, 101 of which were with the Omicron variant and 65 of which were with Delta.

READ ALSO: What to know about Germany’s planned PCR test restrictions

They found that the least reliable tests picked up less than a third of Omicron infections with a high viral load, whereas the same type of tests picked up 70 percent of Delta infections with an equivalent viral load.

In terms of infections with a medium viral load, the tests picked up between zero and eight percent of Omicron infections and between zero and 28 percent of Delta infections.

With some 580 different antigen tests on the market, Keppler said that the Paul Ehrlich Institute – Germany’s medicines agency – should publish a list of which ones are most effective against Omicron.

“The one-eyed among the blind must now be quickly identified and published by the Paul Ehrlich Institute,” he said.

He also called on the public to exercise continued caution.

“You should never take a negative result as a free pass,” Keppler warned, adding that “asymptomatic testing with self-tests makes little sense in my view.”

He said that people should instead rely on measures such as social distancing and wearing masks, while continuing to go for testing in the case of symptoms.

SEE ALSO: German state sets out plan to end Covid tests in schools

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What to know about Germany’s planned PCR test restrictions

According to a recent decision by the German federal and state governments, PCR tests will soon be restricted to high-risk groups and people who work with vulnerable people. But how does this affect things like quarantine rules and measuring infection rates? Here's what we know so far.

Covid test centre in Hamburg
A sign in Hamburg advertises free antigen tests and paid-for PCR tests to the public. Photo: picture alliance/dpa | Daniel Bockwoldt

Why are tests being restricted? 

Germany’s infection rates have been spiralling over the past few weeks, hitting new all-time-highs on a daily basis. At the time of writing on Wednesday, the 7-day incidence of Covid infections was 940 per 100,000 people – a massive jump from the figure of 584 recorded just a week ago. 

In Berlin, the current Omicron hotspot, the 7-day incidence of infections is currently almost 1,800 per 100,000 residents. 

These high incidences are matched by record daily cases. On Wednesday, around 164,000 new Covid infections were reported within a day. But due to limited testing capacities and staffing issues at local health authorities, this could be an underestimation.

Though severe courses of Omicron are believed to be rarer than with the previous dominant variant Delta, experts say that current wave is nowhere near its potential peak. Health Minister Karl Lauterbach (SPD) believes that the country could record as many as 400,000 new cases a day by February. 

Against this backdrop, the government wants to restrict the availability of PCR tests in order to ensure that there are enough tests for people who need them. 

What’s the current testing capacity? 

According to recent data from the Association of Accredited Laboratories in Medicine (ALM), 2.4 million PCR tests were carried out in Germany last week. One in three tests were positive, they confirmed, and the proportion of positive samples is rising week-on-week.

Currently, the laboratories are working at around 95 percent capacity, meaning that just a small increase in infections or staff shortages could lead to testing centres becoming overwhelmed. 

The government has promised to expand these testing capacities to cope with the Omicron wave, but it also wants to introduce restrictions. 

OK, so can I still get a free PCR test? 

Currently, anyone with Covid symptoms, a positive antigen test or a red alert on their Corona Warn app can get one for free on their health insurance or by visiting a state testing centre. 

But this looks set to change. 

In future it will depend on your profession and your health. Only people who fall into a ‘risk’ category – i.e. someone who is elderly or has pre-existing condition – and those who work with vulnerable groups will be able to get a PCR test for free. 

Specifically, the new ordinance mentions staff “in hospitals, in surgeries, in nursing and in institutions for integration assistance”. 

Of course, if you’re happy to pay for one, you may be able to still get a PCR test with a private provider – these tend to cost upwards of €40 per test. 

READ ALSO: KEY POINTS: How Germany will tackle latest phase of the Omicron wave

How does this affect quarantine and self-isolation rules?

That’s a tricky one to answer, since normally a PCR test is required to confirm an infection – but a potential rule-change could be on the cards. In future, people who don’t belong to a risk group could require two positive antigen test results to confirm a Covid infection and self-isolate. 

The same is likely to apply for proving a past Covid infection, though once again nothing concrete has emerged yet. 

Corona Warn App red alert

The Corona Warn App shows a red alert. Photo: picture alliance/dpa | Julian Stratenschulte

In addition to rapid tests, the government is pinning its hopes on so-called Poc-NAAT tests to help bolster its testing capacity. There should soon be one million more of these tests – which are allegedly around 10 times more accurate than rapid tests – available per week. The use of these may be restricted to people with Covid symptoms, but again nothing firm has been worked out yet.  

In terms of getting released from self-isolation, the government is making a tweak to its recently changed quarantine rules. This will mean that people who work in hospitals and care homes will soon be able to use a rapid test to release themselves from quarantine after a week – just like everyone else. Previously, the government had required a PCR test for this group. 


Can we still track Covid figures if we are restricting tests?

That’s a very good question. According to information obtained by the Redaktionsnetwerk Deutschland (RND), the Federal Ministry of Health is currently working with the Robert Koch Institute (RKI) on a new system for calculating infection rates.

Antigen test results are currently forwarded onto the RKI, but are only included in official statistics if accompanied by a positive PCR test result. 

“Whether and in what form antigen tests will be included in the statistics in future is currently being examined,” the RKI told RND.

In other words, it is possible that antigen test results will also be used to help calculate the Covid incidence in future – though the RKI would have to take into account the lower accuracy of these tests in its modelling. 

When are the changes coming into force?

That we don’t know yet. The Health Minister and his state colleagues are still working out the details at the moment so keep in mind that there could be room for slight changes in the finished legislation. 

It is then likely that states would adopt measures, and there can be variations among state regulations.