The SARS-CoV-2 virus (severe acute respiratory syndrome coronavirus 2) poses a global threat that strains the healthcare system to its limits. The pandemic caused by the new coronavirus in recent years has been a major topic and concern for scientists, politicians, and ordinary citizens. The constant fear for oneself and loved ones, affects the psychological and emotional well-being of society, and the economic consequences will be felt for many years to come. Therefore, it is crucial to immediately control the threat.

Given the lack of targeted treatment options, developing immunity is currently the only available method to fight for a return to "normal" life and limit global economic consequences.

The SARS-CoV-2 virus is transmitted via droplets and causes an acute respiratory infectious disease called COVID-19. The incubation period is 2-14 days. Most of infected individuals exhibit mild or asymptomatic infection. A portion of the population, particularly the elderly and those with comorbidities may experience severe course of infection that can lead to death.

The main symptoms of COVID-19 are fever, sore throat, dry cough, and fatigue. Less common, are headaches and dizziness, abdominal pain, nausea, and vomiting. Loss of smell (anosmia), taste, and diarrhoea may also occur. Severe course of COVID-19 is characterized by difficulty breathing, and even the need for assisted breathing. As a result of the disease, among other things, damage or inflammation of the heart muscle, heart attack and heart failure, arrhythmia, venous thromboembolism, disseminated coagulopathy, multi-organ failure, cognitive dysfunction, or acute respiratory distress syndrome (ARDS) may develop.

Risk factors predisposing to a severe course of COVID -19 include age, male gender, cardiovascular diseases, chronic kidney failure, chronic lung diseases, such as, asthma and chronic obstructive pulmonary disease (COPD), uncontrolled diabetes, hypertension, BMI>30, sickle cell anaemia, and smoking.

The risk of contracting the disease, especially the need for hospitalization and the likelihood of death, are significantly reduced in vaccinated individuals. Moreover, according to a study in the US, fully vaccinated people have a 5-fold lower risk of disease and hospitalisation than unvaccinated recoverers.

As a result of SARS-CoV-2 infection, antibodies are produced in the human body directed against the virus antigens. Vaccination aims to induce this response without direct contact with the pathogen. In the case of a past infection, antibodies are produced against, among others, the nucleocapsid (N protein) as well as the spike protein (S protein). Available vaccines are targeted at producing antibodies directed against the S1 domain of the virus protein, which binds to the specific receptor (ACE2) on the cell membrane of human cells. The available literature suggests that the level of antibodies directed against the S protein correlates with the organism's ability to neutralise the virus.

According to the literature, PCR-confirmed SARS-CoV-2 infection occurs in 5-22% of cases without the production of specific antibodies. Asymptomatic and mild course of the disease is associated with an increased likelihood of seronegative results. Literature reports are not consistent as to how long antibody level persists in study groups. Discrepancies in results among demographic groups may be due to the design of individual studies themselves, including a small number of subjects.

Severe course of the disease is mostly associated with the production of a higher level of antibodies against SARS-CoV-2 antigens, however, the kinetics of changes in their concentration is not correlated with the initial value. Similarly, in the case of vaccination, it is not possible to predict how quickly the antibody level will decrease. Nevertheless, these processes can be controlled on an individual basis by performing periodic testing of antibody levels.

The anti-SARS-CoV-2 antibody test is based on the determination of the level of IgG class antibodies directed against the S1 domain of the spike protein and allows for evaluating the immune response obtained after infection or vaccination. The level of antibodies directed against the S protein correlates with the body's ability to neutralize the virus.

The test is performed using an immunoenzymatic method (ELISA) allowing for a quantitative determination of IgG antibodies with a test developed by EUROIMMUN. A linear correlation with the "First WHO International Standard" (NIBSC code: 20/162) was demonstrated, allowing the test to be calibrated in international units.

The advantage of the test is that it can be performed with a variety of materials: serum, EDTA plasma, citrate plasma or from a dried blood spot.

Masdiag Laboratory participates in the proficiency testing program "Antibodies against SARS-CoV-2" organized by IfQ-Lübeck.

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