Kinetics of IgM, IgA, IgG to SARS-CoV-2 in children with COVID-19 in Lviv region in different periods of the infectious process depending on the severity of the course and age

Abstract

Aim. The research aims at analyzing the kinetics of IgA, IgM, and IgG to SARS-CoV-2 in children based on the severity of COVID-19 and age.
 Materials and Methods. The conducted prospective study involved 88 children (mean age 9.4 years) with COVID-19, admitted to the "Lviv Regional Pediatric Clinical Hospital "OKHMATDYT" from 2020 to 2021. The participants included 36 males (40.90%), and 52 females (59.10%) in the observation group. Diagnosis verification relied on clinical manifestations of the disease, with the detection of SARS-CoV-2 RNA from nasal mucus using the PCR method. The values of IgA, IgM, and IgG to S and N proteins of SARS-CoV-2, determined by the ELISA method at different times of the infectious process in 380 blood serum samples, were analyzed.
 Results and Discussion.The research findings of IgM to SARS-CoV-2 in the first week of illness revealed a median value of 0.24 [0.14; 1.39], increasing to 0.49 [0.30; 2.87] in the second week. The highest median value of IgA to SARS-CoV-2 is 0.33 [0.24; 1.00] was found from 15 to 30 days, after 30 days it was 0.24 [0.20; 0.28].
 The increase in the median value of IgG-N to SARS-CoV-2 was observed from the second week of the illness, reaching 1.13 [0.52; 3.17], with its maximum value at 5.68 [2.39; 8.86] within the period up to three months. Severe COVID-19 was diagnosed in 27 children (30.68%), comprising 15 females (55.56%) and 12 males (44.44%). In the majority of hospitalized children, IgM values at different degrees of disease severity were positive from the first to the seventh day of illness. In children with a severe course of SARS-CoV-2, the median value of IgM in blood serum during this period was 1.39 [1.36; 4.07]. There was a statistically significant difference between the IgG levels for moderate and severe forms on days 15-30 of the illness: 0.54 [0.21; 1.89] compared to 5.55 [4.99; 5.80], respectively (p<0.05). In patients with both moderate and severe forms of the disease, median values of IgG to N SARS-CoV-2 were positive throughout the study period. A significant increase in the median value of IgG to N SARS-CoV-2 was observed in females from day 31 to day 90. In severe cases of the disease, the median value of IgG to SARS-CoV-2 from three to six months was 9.40 [7.80; 10.60], which was higher than in patients with a moderate form of the disease - 8.72 [8.64; 8.97] (p<0.05).
 Conclusions. Serological studies enable the investigation of the immune response to SARS-CoV-2, determination of seroconversion, and characterization of the course of COVID-19, being crucial for epidemiological research. The levels of IgM, IgA, and IgG to SARS-CoV-2 depend on the disease's severity and the patient's age.