A Prospective Analysis of Sustained Immunity Following Covishield Vaccination

Abstract

Introduction: The outbreak of Coronavirus Disease 2019 (COVID-19) affected a large number of people worldwide within a short period of time. The mortality rate was high, and there was no specific medicine available to cure it. Therefore, the situation demanded the rapid development of a vaccine. When the vaccines were introduced, there was limited knowledge about their efficacy, side-effects, and duration of protection. Hence, a detailed study was conducted in these areas. Aim: To study the immunological responses following Covishield vaccination and determine the duration of protection offered by the vaccine. Materials and Methods: The present study is a prospective observational study conducted at Sree Balaji Medical College and Hospital, Chennai, Tamil Nadu, India from March 2021 to May 2023, involving the staff members of the hospital and college who were above 18-year-old. Individuals with immunodeficiency, those on immunosuppressive medication, or anyone with proof of COVID-19 were excluded. The total sample size was 56. Blood samples were collected before administering the vaccine, at 0, 3, and 12 months, and tested for Complete Blood Count (CBC), COVID-19-specific Immunoglobulin G (IgG), Cluster of Differentiation (CD) 45, CD3, CD4, CD8, etc. The findings were statistically analysed using Statistical Packages of Social Sciences (SPSS) software version 22.0 and STATA software version 10. Results: A total of 154 volunteers initially provided the first blood samples. However, only 129 of them provided blood samples 2nd time and received two doses of the vaccine. Out of these, only 56 participants completed the fourth time blood test. The results consistently demonstrated a rise in IgG levels over time, with consistently higher levels observed in females. Participants above 45 years exhibited higher IgG levels. Individuals with co-morbidities also showed an increase in IgG levels. The research revealed that individuals who were initially IgG negative experienced a greater fold increase in IgG levels after the first dose of vaccination. The incidence and duration of side-effects post-vaccination reduced with each successive vaccine dose. Conclusion: All the volunteers developed adequate IgG antibodies. Two doses of Covishield effectively resulted in lasting immunity in 94.64% of cases, and three doses achieved 100% immunity. Females and participants above 45 years consistently exhibited higher antibody levels. Individuals with co-morbidities also developed antibodies, albeit at slightly lower levels. The side-effects were mild and short-lived. No long-term after effects were detected even after two years and two months following vaccination.