Immune Response in Repeated Covid-19 Infections Differences by Age Group

Abstract

Repeated infection with SARS-CoV-2 allows us to evaluate the body's immune memory response and its effectiveness in defense against infection. Age is an important factor affecting the intensity of the immune response in COVID-19. The aim of the present study was to compare the immune response to a recurrent episode of COVID-19 in patients of different age groups.  Unvaccinated patients (n=140) with confirmed first and second episodes of SARS-CoV-2 infection, divided into four age categories (<18, 18-49, 50-64 and ≥65 years) were included in the study; indices of humoral immunity (titres of specific IgG antibodies) and cellular immunity (number of virus-specific T-lymphocytes) were studied several weeks after each episode of disease.In young individuals, re-infection was found to result in a significant increase in antibody levels (~2-fold increase in titre on average) and an enhanced T-cell response, whereas in elderly patients the increase in immune response was significantly less pronounced. The young groups had higher mean antibody titres and higher numbers of specific T cells after both the first and second infection compared to the elderly (differences statistically significant, p<0.05). Thus, the immune response to recurrent COVID-19 varies considerably according to age: the young have a stronger and more effective immune response that provides better protection against reinfection, whereas the elderly have a weakened immune response that may increase the risk of recurrent severe disease.