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Before the end of this month, the Swiss pharmaceutical company Roche plans to launch a rapid test that can detect if someone is infected with Sars-CoV-2 in just 15 minutes. Then it should also be available in Germany in early October. Similar to a pregnancy test, a test strip must show a positive or negative result directly. The company plans to produce around 40 million tests per month.
The announcement sounds like the next great hope: You could test in emergency rooms or before visiting nursing homes. In a next step, maybe even before concerts or football games, because if only those who tested negative got together, big events should be possible again, right?
The new test works differently than previously known testing procedures, that’s true. However, it will not be freely available in pharmacies, nor do the results seem significant enough to be used across the board. The summary.
How does the Roche rapid test work?
Roche’s new test is an antigen test. According to the manufacturer, similar to the PCR test, you can evaluate nasopharyngeal smears. While the polymerase chain reaction (PCR) increases the RNA of the virus and thus detects the genetic material, if present, the antigen test looks for the typical proteins of the virus.
To do this, a sample is taken from the nasopharynx with a swab and placed on a test strip with antibodies to Sars-CoV-2. “If antigens are present in a sufficient concentration, they bind to antibodies,” Roche writes in a press release. After about 15 minutes a positive or negative result will be displayed.
Since it is very difficult to get deep enough into the throat even with the test stick, the sample can only be taken by trained medical personnel. Therefore, the quick test is not suitable for home use.
How reliable is the new rapid test?
Only the note “if antigens are present in sufficient concentration” suggests that the test is prone to errors. Because apparently this needs enough antigens in a sample to recognize it as positive. However, it is now known that especially patients with mild courses often have a lower viral load, and therefore also a lower concentration of antigens. It is questionable whether the test also detects asymptomatic patients or those with mild symptoms. Furthermore, the quality of the sampling is decisive for the accuracy of the test result.
The manufacturer himself gives the sensitivity, that is, the probability with which the test actually recognizes sick people as sick, of 96.52 percent. Therefore, the Roche test gives a false negative result in about 4 out of 100 patients. For comparison: the sensitivity of the PCR tests used in Germany is between 95 and 100 percent. Due to the generally low sensitivity of antigen tests, the group itself recommends taking other factors into account when interpreting negative test results, such as the patient’s symptoms or contact with someone who has Covid-19. An additional validation test is also possible.
The specificity, that is, the probability with which really healthy people are recognized as such, is 99.68 percent, according to Roche.
What are antigen tests useful for?
Some scientists have high hopes for the development of a reliable antigen test. Like PCR, it could detect an active infection and thus help break the chains of infection. Antigen testing has considerable advantages over PCR: on the one hand, it can be tested in the so-called points of care, that is, in situ, it can be used and evaluated. The samples do not have to be sent to the laboratory and then evaluated in detail there. In principle, this could save staff, time and money. On the other hand, the required test material is cheaper. The group does not want to disclose how much cheaper: “We do not disclose details about the prices, but we design the prices so that costs do not represent a barrier to access our tests,” Roche said at the request of SPIEGEL.
Roche itself sees its test as an important contribution to the fight against the pandemic. It can be used with symptomatic and asymptomatic people, where quick decisions need to be made, according to the company’s announcement. “It serves as a valuable first screening test for people who have had contact with infected people or who have been in higher risk places.”
It would be conceivable for use in returnee testing centers at airports or train stations. Returning travelers would know within 15 minutes if they need to be quarantined or if they can safely take public transportation home. Nursing home staff or visitors could also be tested regularly before entering the facility to ensure that they do not introduce the virus and thus endanger risk groups. It could also be used in hospital emergency rooms, where decisions often need to be made quickly about how to treat patients.
So will they soon replace slow PCR tests?
Caution should be exercised when using antigen tests due to their poor reliability. Because each false negative result could give the person being tested a false sense of security and could cause a new outbreak. This would be fatal, especially in facilities with risk groups, such as nursing homes.
As Roche itself writes, negative antigen test results must be accurately interpreted and, if necessary, rechecked with another test. This in turn would mean that the PCR would be needed again.
However, antigen testing is not superfluous. For example, by testing groups like the employees of a meat factory, they could at least provide a rough guide to whether or not most were infected. Because if you test a greater number of people, at least according to statistics, the probability that many infected people will also be found is higher. This would allow you to react a little faster to new outbreaks than is currently possible with the PCR method, where you often wait four days for the result.
However, antigen testing is not suitable for re-allowing important events or for visiting grandparents without hesitation.
