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Introduction. Recently, the world community and modern medical science have faced the challenge of the emergence new human coronavirus SARS-CoV-2 capable of causing severe acute respiratory syndrome. WHO has named the disease caused by this virus Covid-19 (coronavirus infection disease). SARS-CoV-2 was first detected in December 2019 in Wuhan, from where it quickly spread to China and further around the world. Due to the high contagiousness and pathogenicity of SARS-CoV-2, WHO declared the global pandemic Covid-19 in early March 2020. The features of the pathogenesis of Covid-19 determine the significant frequency cases of this disease with a severe course. The severity course of the disease and the consistency and completeness of the immune response are interrelated: excessive and continued activation of innate immunity factors with an increase in the cytokine profile is observed in patients with severe course, and the transition to the stage of production the specific antibodies is characterized by an improvement in the patient's condition and recovery. The specific humoral response is important in the formation of collective post-infection and post-vaccination immunity and is an indicator of overcoming epidemic processes in the population. The study is conducted in the Mechnikov institute of microbiology and immunology National Academy of Medical Sciences of Ukraine has one of the tasks of determining specific antibodies to SARS-CoV-2 in different age groups and monitoring the formation of the immune layer during the epidemic process, as well as the duration of detection of specific antibodies. Material & methods. A study was conducted to determine specific total immunoglobulins, IgA, IgM and IgG to SARS-CoV-2 by enzyme-linked immunosorbent assay (ELISA) among schoolchildren Kharkiv gymnasium №X for 27-28 weeks of the pandemic (21-24/09/2020). The object of the study were 439 samples of serum from children aged 6 to 16 years. Results & discussion. This phase of the study the presence of specific SARS-CoV-2 antibodies in certain groups held at a time when the territory of Ukraine still it was not observed a significant increase in the number of patients with Covid-19 compared to Western Europe, China, the USA and others, but with almost 6 months have passed since the beginning of the pandemic. Most of the patients (98.4 %) in a survey questionnaire and not noted the manifestations of acute respiratory illness, excessive fatigue, temperature rise or other manifestations characteristic of Covid-19. The study revealed total SARS-CoV-2 antibodies in 20.3% of children, questionable levels total antibodies were found in almost 9 %. IgA was detected (positive and questionable) in 15.2 % of children, IgM – 7.7 %, and IgG – 14.3 %. In serum samples total SARS-CoV-2 antibody positive/questionable in 23.6% of cases were identified only one of the classes of immunoglobulins: IgA at 5,6 %, IgM – 3,3 %, IgG – 14,7 %. In most samples two classes of antibodies were detected simultaneously – 67.4 % of samples and in 9.02% all three classes of immunoglobulins were detected simultaneously. An interesting fact is predominantly simultaneous presence in serum IgA and IgG in 60 samples (46.9%) with total serum antibodies to SARS-CoV-2. Simultaneous detection IgM and IgG was noted much less, only in 29 samples – 22.7%, the combination of simultaneous presence IgA and IgM without presence IgG was detected in one sample (0.78%). Conclusion. The data obtained indicate that more than 20% of school-age children in the randomized sample had antibodies to SARS-CoV-2 at 27-28 weeks of the pandemic (21-24/09/2020), despite the fact that at the time of this study, our country has not yet faced an avalanche of rising morbidity, which was observed in this period. Covid-19 is known to be milder, asymptomatic or asymptomatic in children, which is consistent with our lack of evidence in most children for 6-8 weeks prior to the study, although it is possible to assume that the infection occurred earlier. However, the simultaneous presence in the serum SARS-CoV-2 IgA and IgG in 60 samples (46.9%) and IgM and IgG in 29 samples – in 22.7%, which is approximately three quarters of all children, which had positive antibodies to SARS-CoV-2, according to traditional notions about the frequency of the formation humoral response suggests a higher probability of infection during this period to the coin determination of antibodies in blood serum. Obtained in this study data provide an understanding certain features of the formation SARS-CoV-2 post infectious immunity in school-age children and delivered important issues that require further research.Keywords: Covid-19 school-age children; antibodies to SARS-CoV-2, Introduction. Recently, the world community and modern medical science have faced the challenge of the emergence new human coronavirus SARS-CoV-2 capable of causing severe acute respiratory syndrome. WHO has named the disease caused by this virus Covid-19 (coronavirus infection disease). SARS-CoV-2 was first detected in December 2019 in Wuhan, from where it quickly spread to China and further around the world. Due to the high contagiousness and pathogenicity of SARS-CoV-2, WHO declared the global pandemic Covid-19 in early March 2020. The features of the pathogenesis of Covid-19 determine the significant frequency cases of this disease with a severe course. The severity course of the disease and the consistency and completeness of the immune response are interrelated: excessive and continued activation of innate immunity factors with an increase in the cytokine profile is observed in patients with severe course, and the transition to the stage of production the specific antibodies is characterized by an improvement in the patient's condition and recovery. The specific humoral response is important in the formation of collective post-infection and post-vaccination immunity and is an indicator of overcoming epidemic processes in the population. The study is conducted in the Mechnikov institute of microbiology and immunology National Academy of Medical Sciences of Ukraine has one of the tasks of determining specific antibodies to SARS-CoV-2 in different age groups and monitoring the formation of the immune layer during the epidemic process, as well as the duration of detection of specific antibodies. Material & methods. A study was conducted to determine specific total immunoglobulins, IgA, IgM and IgG to SARS-CoV-2 by enzyme-linked immunosorbent assay (ELISA) among schoolchildren Kharkiv gymnasium №X for 27-28 weeks of the pandemic (21-24/09/2020). The object of the study were 439 samples of serum from children aged 6 to 16 years. Results & discussion. This phase of the study the presence of specific SARS-CoV-2 antibodies in certain groups held at a time when the territory of Ukraine still it was not observed a significant increase in the number of patients with Covid-19 compared to Western Europe, China, the USA and others, but with almost 6 months have passed since the beginning of the pandemic. Most of the patients (98.4 %) in a survey questionnaire and not noted the manifestations of acute respiratory illness, excessive fatigue, temperature rise or other manifestations characteristic of Covid-19. The study revealed total SARS-CoV-2 antibodies in 20.3% of children, questionable levels total antibodies were found in almost 9 %. IgA was detected (positive and questionable) in 15.2 % of children, IgM – 7.7 %, and IgG – 14.3 %. In serum samples total SARS-CoV-2 antibody positive/questionable in 23.6% of cases were identified only one of the classes of immunoglobulins: IgA at 5,6 %, IgM – 3,3 %, IgG – 14,7 %. In most samples two classes of antibodies were detected simultaneously – 67.4 % of samples and in 9.02% all three classes of immunoglobulins were detected simultaneously. An interesting fact is predominantly simultaneous presence in serum IgA and IgG in 60 samples (46.9%) with total serum antibodies to SARS-CoV-2. Simultaneous detection IgM and IgG was noted much less, only in 29 samples – 22.7%, the combination of simultaneous presence IgA and IgM without presence IgG was detected in one sample (0.78%). Conclusion. The data obtained indicate that more than 20% of school-age children in the randomized sample had antibodies to SARS-CoV-2 at 27-28 weeks of the pandemic (21-24/09/2020), despite the fact that at the time of this study, our country has not yet faced an avalanche of rising morbidity, which was observed in this period. Covid-19 is known to be milder, asymptomatic or asymptomatic in children, which is consistent with our lack of evidence in most children for 6-8 weeks prior to the study, although it is possible to assume that the infection occurred earlier. However, the simultaneous presence in the serum SARS-CoV-2 IgA and IgG in 60 samples (46.9%) and IgM and IgG in 29 samples – in 22.7%, which is approximately three quarters of all children, which had positive antibodies to SARS-CoV-2, according to traditional notions about the frequency of the formation humoral response suggests a higher probability of infection during this period to the coin determination of antibodies in blood serum. Obtained in this study data provide an understanding certain features of the formation SARS-CoV-2 post infectious immunity in school-age children and delivered important issues that require further research. Keywords: Covid-19 school-age children, antibodies to SARS-CoV-2DOI: 10.5281/zenodo.4382196