German study proves inaccuracy of rapid antigen tests for variants, medium to low viral loads

 . The COVID-19 Antigen Study (COVAG Study), conducted by SYNLAB, the Universities of Heidelberg and Graz, and a large

    COVID-19 test centre in Stuttgart, is one of the most comprehensive systematic evaluations of rapid antigen testing 
    in a real-life setting 
  . The COVAG Study confirms a significantly lower accuracy of rapid antigen tests compared to PCR tests, determining 
    the actual sensitivity of rapid antigen tests at about 60 percent 
  . Study results imply that rapid antigen tests have a lower sensitivity when testing for new virus variants 
  . Effectiveness of rapid antigen tests as a tool to control the pandemic is limited 

SYNLAB, Europe's leading medical diagnostic services provider, collaborated with researchers from the Universities of 
Heidelberg and Graz, and a large COVID-19 test centre in Stuttgart to conduct the COVID-19 Antigen Study (COVAG Study). 
The COVAG Study is one of the most comprehensive field research studies to systemically assess the actual sensitivity 
and specificity of rapid antigen tests. 
The results indicate that the actual sensitivity of two commonly used rapid antigen tests considered reliable, are only 
at 60.4 and 56.8 percent, respectively, compared to PCR tests. In addition, for the first time the COVAG Study 
identified a variant-dependency of rapid antigen tests: the sensitivity of the tests is significantly lower when 
detecting the alpha variant compared to their sensitivity when detecting the SARS-CoV-2 wild-type. 
338 out of 2,215 individuals participating in the study tested positive for SARS-CoV-2 using the PCR testing method. Of 
these 338 positive cases, however, the two rapid antigen tests only identified 204 and 192 participants, respectively, 
as virus carriers. In other words, rapid antigen tests missed four out of ten individuals who tested positive for 
SARS-CoV-2 with PCR tests. Here, the viral load was the most decisive factor for the detection of the virus. Only 
individuals with a very high viral load (CT value <= 20) were reliably detected as virus carriers by rapid antigen 
tests. The virus, however, already spreads at a medium to low viral load. 
In addition, the COVAG Study was the first to investigate variant dependence of rapid antigen tests in samples with 
moderate to high viral loads (CT value <= 30). For the SARS-CoV-2 wild-type, the two rapid antigen tests' sensitivity 
was determined with 87.7 and 84.0 percent, respectively. Yet, for the alpha variant the same tests' sensitivity was 
only at 77.1 and 72.3 percent, respectively. Compared to other circulating variants, however, the alpha variant has the 
lowest structural deviation from the SARS-CoV-2 wild-type. Accordingly, it can be assumed that the sensitivity of rapid 
antigen tests is also significantly lower for other virus variants than for the original wild-type. Meanwhile, however, 
the latter has been completely displaced by the spread of new variants. 
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