A Prospective Multicenter Randomized Study State of Humoral Immunity after a New Coronavirus Infection (COVID-19) of a Mild or Asymptomatic Course

Background. The rapid spread of COVID-19 in the world, the severity of disease, high morbidity and mortality have rightly made the COVID-19 pandemic a major threat to humanity. Therefore, one of the most urgent problems for practical health care is the issue of development of immunity for COVID-19 survivors, the possibility of re-infection, and the appropriateness of vaccination. The article presents the interim results of the study was named “RESPONSE” devoted to assessing the immunity for 90 days from patients that survived COVID-19 in a mild or asymptomatic course. 

Aims — to study of the dynamics of generation of SARS-CoV-2 adhesive (S) protein neutralizing antibodies (IgG) and specificities of humoral immunity from COVID-19 survivors with light and asymptomatic form of disease in depending on gender and age. 

Materials and methods. Joint study by the Military Medical Academy n.a. S.M. Kirov and Laboratory Service “Helix” is being undertaken in the period from January 06, 2020 to August 1, 2021 on the basis of Academy clinics and Helix diagnostic centers in Saint Petersburg. The study was included 1109 males and females aged 18 to 70 (average age 38.2), who received to outpatient treatment of light and asymptomatic form of New Coronavirus Infection. All patients included in the investigation were done survey of quantitative neutralizing antibodies of class IgG to S-protein SARS-CoV-2 content in venous blood in 30, 45, 60 and 90 days from the last result of positive polymerase chain reaction with reverse transcription (OT-PCR) for determining nucleic acid SARS-CoV-2 in biological material by immunochemiluminescent analysis (LIAISON XL, DiaSorin S.p.A., made in Italy). 

Results. The IgG class antibody to the S-protein SARS-CoV-2 were not diagnosed 30 days after the survived infection only 0.9% of young women (18–44 years) and 0.8% of men in the same age bracket. In other age groups, antibodies were defined in all participants of study. Titer of IgG gradually increases to peak concentration after 45 days, it’s kept at this level to the 60th day, and then it has a decreasing trend after 90 days from the onset of the disease. 

Conclusions. The results show the timing of generation and duration of the humoral response in survived patients COVID-19 in a mild or asymptomatic form. For 45 days, antibodies were determined in all participants of the study, reflecting the development of post-infectious humoral immunity, which was maintained in patients with the mild or asymptomatic forms of COVID-19 at least 3 months.