• Frequently asked questions on SARS-CoV-2 and the COVID-19 diagnostics

Below, you can find the answers for frequently asked questions about SARS-CoV-2 and the EUROIMMUN tests for the diagnostics of COVID-19


What are coronaviruses?

Coronavirus constitute a large family of viruses which can infect humans as well as animals, for example birds and mammals. Coronavirus infection can lead to a simple cold, but also to severe or even fatal disease. The two highly pathogenic viruses SARS-CoV and MERS-CoV cause severe respiratory syndromes in humans. Infections with the other four human pathogenic coronaviruses (HCoV-NL63, HCoV-229E, HCoV-OC43 and HKU1) mainly only result in mild diseases of the upper respiratory tract. In babies, infants and elderly people, however, the infection can take a severe course.

How is SARS-CoV-2 transmitted?

SARS-CoV-2 is mainly transmitted via aerosols during coughing or sneezing or at close contact with an infected person. Health care personnel and family members are among the high-risk populations.

What are the symptoms of COVID-19?

The symptoms of SARS-CoV-2 infection are fever, coughing, breathing difficulties and fatigue. Most patients suffer from a mild febrile illness with irregular lung infiltrates. Some patients, particularly elderly or chronically ill persons, develop severe acute respiratory distress syndrome (ARDS), which is fatal in three percent of cases. In February 2020, the disease caused by SARS-CoV-2 was named COVID-19 (coronavirus 19) by the WHO.

How is a person tested for COVID-19?

Laboratory tests for the diagnosis of SARS-CoV-2 infection include polymerase chain reaction (RT-PCR) with smears from the upper and lower respiratory tract (bronchoalveolar lavage fluid, tracheal secretion, sputum, nasopharyngeal secretion, oropharyngeal secretion, etc.) for direct detection of the virus. The test is used for primary laboratory diagnostic examination of patients with suspected SARS-CoV-2 infection. Additionally, there are serological tests for the detection of antibodies against SARS-CoV-2 in the blood. The antibody test is the ideal supplement to direct detection. It supports the diagnosis of SARS-CoV-2 infection and helps to confirm the RT-PCR results. Moreover, the determination of antibodies is relevant for the clarification of suspected cases of SARS-CoV-2 without symptoms or with negative results in direct detection. In addition to their importance for diagnostics, serological tests can also be used to gather epidemiological data and for outbreak control. 

Where can I find further information on SARS-CoV-2 and COVID-19?

World Health Organisation (WHO) https://www.who.int/

European Centre for Disease Prevention and Control (ECDC) https://www.ecdc.europa.eu/en/home 

EUROIMMUN tests for COVID-19 diagnostics

Are the SARS-CoV-2 tests from EUROIMMUN approved?

The EURORealTime SARS-CoV-2, the Anti-SARS-CoV-2 ELISA (IgA and IgG), the Anti-SARS-CoV-2 NCP ELISAs (IgG and IgM) and the Anti-SARS-CoV-2 QuantiVac ELISA (IgG) are CE-marked and can be used for COVID-19 diagnostics. The Anti-SARS-CoV-2 ELISA (IgG) and the EURORealTime SARS-CoV-2 were approved by the U.S. food and drug administration (FDA) through an emergency use authorization (EUA) for use by authorised laboratories. The Anti-SARS-CoV-2 ELISA (IgG) is also approved by the Brazilian Health Regulatory Agency ANVISA.

Where can you get tested?

Our tests are exclusively performed in the laboratory. The required samples (blood, swabs...) are taken by a physician, e.g. your GP, and then sent to the respective laboratory in charge.

If you are interested, please get in touch with the Clinical Immunological Laboratory Prof. Dr. med. Winfried Stöcker (Seekamp 31, D-23560 Lübeck) which performs the tests.

Where can you buy our tests for COVID-19 diagnostics?

With the Anti-SARS-CoV-2 ELISAs (IgA and IgG), EUROIMMUN was one of the first companies to offer CE-marked test systems for the detection of antibodies against SARS-CoV-2 already from mid-March 2020. Our range of antibody tests for COVID-19 diagnostics has now been extended by the CE-marked Anti-SARS-CoV-2-NCP ELISA (IgG, IgM) and the Anti-SARS-CoV-2 QuantiVac ELISA (IgG). Our PCR test EURORealTime SARS-CoV-2 is also CE-marked. Both the ELISAs and the PCR test are designed to be used in diagnostic laboratories and are currently only despatched for this cause. They are not rapid tests for at-home testing.

If you wish to receive a quote for our tests, please contact your local distributor.

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Can private persons perform the tests?

Please note that our assays are not rapid tests for at-home testing. Our ELISAs are designed for the investigation of large samples volumes and their processing requires laboratory equipment. Our PCR test is designed for use in the laboratory. Cassette-based rapid tests for at-home use may present technical limitations such as reduced sensitivity or specificity. We therefore do not offer rapid tests.

If you suspect to be infected with SARS-CoV-2, please ask your physician for a laboratory diagnostic test.

What are the application areas for the RT-PCR (direct pathogen detection) and the ELISAs (antibody detection) in COVID-19 diagnostics?

Direct pathogen detection via RT-PCR is the method of choice to detect acute COVID19 infections. PCR allows for detection a few days after infection as well as in subclinical/asymptomatic infections. The virus can be detected within a time window of 10-14 days after onset of symptoms. However, when the immune reaction starts and the viral load diminishes, the sensitivity of direct detection tests decreases. The pathogen can then no longer be detected in every patient.

Serological testing (serology), i.e. the detection of antibodies, expands the diagnostic window over the first one to two weeks. Serology allows identification of persons with a persisting (no longer acute) or past infection with SARS-CoV-2.

Moreover, the S1 domain of the spike protein used in the Anti-SARS-CoV-2 ELISA and Anti-SARS-CoV-2 QuantiVac ELISA contains the receptor binding site (RBD) of SARS-CoV-2 via which the virus binds to the human cells. Especially IgG antibodies against the S1 domain/RBD could therefore have a virus-neutralising and thus protective function.



At what time after infection can the RT-PCR or the ELISAs be applied?

The WHO estimates an incubation period of 1 to 14 days for SARS-CoV-2, in most cases, approximately 5 days. This is the time that passes between the contact with the virus and the onset of first symptoms.

Even though there are no extensive studies available yet, it is assumed that the virus can be detected directly after symptom onset, in swabs of the lower respiratory tract, by means of RT-PCR.


In viral infections, antibodies are generally only produced at least one week, frequently two weeks after onset of symptoms and are detectable only then. Specific IgG antibodies can be detected with high sensitivity using the Anti-SARS-CoV-2 ELISA (IgG) or the Anti-SARS-CoV-2 NCP ELISA (IgG)from approximately day 10 after symptom onset. IgG against the nucleocapsid protein (NCP) often occur some days prior to the anti-S1 IgG antibodies. A positive test result confirms virus contact. The Anti-SARS-CoV-2 ELISA (IgA) and the Anti-SARS-CoC-2 NCP ELISA (IgG) are both suitable for early monitoring of an immune response after positive direct detection, when specific IgG antibodies have not yet been produced.

Do the test results allow drawing conclusions on infectiousness or immunity?

As long as the virus can be detected in the secretions of the respiratory tract by means of PCR, the patient is assumed to be infectious.

The ELISA technique cannot show whether the detected antibodies have a neutralising effect on the pathogen or not. Whether the IgG results obtained by ELISA may allow drawing conclusions on the immunity of a patient is currently investigated by scientific research. Generally, however, it can be assumed that immunity is associated mainly to class IgG antibodies as are detected by our Anti-SARS-CoV-2 ELISA (IgG) and Anti-SARS-CoV-2 QuantiVac ELISA (IgG). These are based on the S1 domain of the spike protein, including the immunologically relevant receptor binding domain (RBD) as the antigen. Please find further information here. This is also indicated by many published results as, for instance, from the so-called “Heinsberg Study” by the University of Bonn. The study underlines the high quality of the Anti-SARS-CoV-2 ELISA (IgG) and shows that the ELISA correlates very well with neutralisation assays.

Can the tests distinguish SARS-CoV-2 infection from infections with other coronaviruses?

EURORealTime SARS-CoV-2: Yes. Due to the detection of two specific gene sequences of the virus, SARS-CoV-2 infections can be reliably identified and delimited from other coronavirus infections.

Anti-SARS-CoV-2 ELISA/Anti-SARS-CoV-2 QuantiVac ELISA/Anti-SARS-CoV-2 NCP ELISA: In the validation of the ELISAs, no cross-reactions to antibodies against worldwide distributed coronaviruses were observed. However, cross-reactions between SARS-CoV(1) and SARS-CoV-2 cannot be excluded due to the close relationship of these two viruses.

Which laboratory equipment is required for performance of the SARS-CoV-2 ELISAs (IgA and IgG), the Anti-SARS-CoV-2-NCP ELISA (IgG) and the EURORealTime SARS-CoV-2?

Anti-SARS-CoV-2 ELISA/Anti-SARS-CoV-2 NCP ELISA: Photometer, 37°C incubator; The test kits include a 96-well ELISA plate (individual break-off wells, enabling adjustment to the actual number of samples to be analysed) and contain all reagents and control materials required for the test performance. Depending on the number of calibrators, up to 93 patient samples can be analysed with one test kits. Like other ELISAs, the test kits can be performed manually. Of course, the ELISAs can be processed fully automatically on our EUROIMMUN Analyzer I and I-2P (Analyzer I: up to 7 microplates, up to 180 samples per test run) and the EUROLabWorkstation ELISA (up to 15 microplates, up to 696 samples per test run).

EURORealTime SARS-CoV-2: The test is compatible with the standard equipment (real-time PCR thermocycler) present in most of the molecular-diagnostic laboratories. The EURORealTime SARS-CoV-2  was validated on the following real-time-PCR cycler: 7500 Fast Real-Time PCR Instrument (Applied Biosystems), LightCycler® 480 II (Roche), CFX 96 Touch (Bio-Rad), RotorGene Q (Qiagen), qTower3 (Analytik Jena).If other cyclers are used, they must validated by the customers themselves.

Which RNA extraction methods can be used for the EURORealTime SARS-CoV-2?

RNA extraction can be performed by any method (automated or manual) which is suited and validated for the sample materials. The EUROrealTime SARS-CoV-2 test was validated with the QIAamp Viral RNA Mini Kit (Qiagen), the NucleoMag® VET Kit (Macherey-Nagel) and the CMG-2015 Prepito Viral DNA/RNA200 Kit (Chemagen).

Which sample materials can be used for the EURORealTime SARS-CoV-2?

Validation of the EURORealTime SARS-CoV-2 test was based on RNA preparations of pharyngeal swabs. Other sample materials / sources of RNA can be used as well, but have to validated by the customer.

How long does it take to get the results?

Here, the shipping times of the sample to the laboratory and the capacities of the laboratory must be taken into account. The sole test performance is around 2 hours with the ELISAs and approximately 1.5 hours with the EURORealTime SARS-CoV-2.

Which antigen is applied in the Anti-SARS-CoV-2 ELISAs (IgA and IgG), the Anti-SARS-CoV-2 QuantiVac ELISA (IgG) and the Anti-SARS-CoV-2-NCP ELISA (IgG and IgM)?

The Anti-SARS-CoV-2 ELISAs (IgA and IgG) and the Anti-SARS-CoV-2 QuantiVac ELISA (IgG) are based on the S1 domain of the spike protein (S) which is produced in a sophisticated procedure with a human cell line. This procedure allows representation of complex three-dimensional structures and post-translational glycosylations. Therefore also antibodies can be detected which exclusively react with authentic epitopes of SARS-CoV-2. Due to the use of this antigen, the Anti-SARS-CoV-2 ELISAs (IgA and IgG) and the Anti-SARS-CoV-2 QuantiVac ELISA (IgG) can detect antibodies with high specificity and sensitivity. Moreover, the S1 domain contains the receptor binding site (RBD) of SARS-CoV-2 via which the virus binds to the human cells. Especially IgG antibodies against the S1 domain/RBD could have a virus-neutralising and thus protective function (the question of immunity is still subject of intensive research).

The Anti-SARS-CoV-2 NCP ELISAs (IgG and IgM) are based on a modified variant of the particularly immunogenic viral nucleocapsid protein (NCP). Antibodies against the nucleocapsid protein are typical markers for infections with SARS-CoV-2. The nucleocapsid protein in its full length, however, presents many homologies within the coronavirus family, which is why the occurrence of unspecific (false-positive) reactions with antibodies against other worldwide circulating human pathogenic coronaviruses cannot be excluded. Therefore, the EUROIMMUN Anti-SARS-CoV-2-NCP ELISAs (IgG and IgM) are based on a designer antigen in which unspecific conserved regions are eliminated, instead of the complete protein.

What are the kinetics of the different antibodies against SARS-CoV-2?

Antibodies develop approx. 1-2 weeks after onset of symptoms. The course of the immune response may vary significantly between patients. Usually, antibodies against the viral nucleocapsid protein (NCP) are produced earlier (approx. 7 days after symptom onset) than the antibodies against the spike protein (S/S1 domain) (approx. 10 days after symptom onset). Antibodies of immunoglobulin class A (IgA) and M (IgM) often occur earlier than those of class G (IgG). IgA and IgM indicate the starting immune response, while IgG antibodies most probably play a role in the development of immunity. Especially IgG antibodies against the S1 domain of the spike protein could have a virus-neutralising and thus protective function (the question of immunity is still subject of intensive research).

Moreover, in the literature examples of individual patients have been described in whom the secretion of antibodies only starts with a time delay of several weeks or even not at all. These patients are negative for anti-SARS-CoV-2-IgG and reduce the clinical sensitivity of serological tests.