ABSTRACT
Background & objectives: Vaccination against COVID-19 induces spike protein-binding IgG antibodies, a robust correlate of protection against COVID-19. This study was undertaken to assess the humoral response after completion of both the doses of ChAdOx1 nCoV vaccine in healthcare workers (HCWs) at a tertiary care health centre in India. Methods: A cross-sectional COVID-19 vaccine-induced antibody study was conducted among HCWs. IgG antibodies against spike protein were measured at least 28 days after the first dose and the second dose of vaccination in both SARS CoV-2 naïve and recovered HCWs. Mean and median antibody titre following each dose of vaccine and its association with age, gender, co-morbidities and factors such as exercise, stress and sleep deprivation were also explored. Results: Among the 200 vaccine recipients, 91.5 per cent showed seroconversion after the first dose and 99.5 per cent after the second dose. The mean titre after the second dose was significantly higher when compared to the first dose (12.68±4.17 vs. 9.83±6.3, P=0.001). More than half (54%) had high antibody titre ≥12 S/Co (Signal/cut-off). Previous COVID-19 infection was the single most important factor influencing antibody production, where the mean titre just after a single dose [mean-17.81±5.94, median-20.5 (interquartile range [IQR]-3.7)] surpassed the titre after the second dose in SARS CoV-2 naïve individuals [mean-12.29±4.00, median-12.8 (IQR-3.7), P=0.001]. Furthermore, 28 per cent of vaccinees showed a reduction in titre after the second dose. The mean fall in titre was 2.25±1.40 and was more pronounced in males, the younger age group and those with previous COVID-19 infection. Interpretation & conclusions: ChAdOx1 nCov-19 vaccine after two doses elicited an excellent immune response. However, greater immunogenicity after the first dose was seen among those with previous COVID-19 infection, even surpassing the titre achieved by the second dose of vaccine in SARS CoV-2 naïve recipients. A fall in antibody titre after the second dose is a matter of concern and requires further studies.
ABSTRACT
Background: COVID-19 vaccines, we believe, have come to rescue us from the clutches of the dreaded severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). With rapid ongoing mutations, it is difficult to predict the effectiveness of seroconversion following vaccination. This study aims to find out the proportion of people with seroconversion following first dose of Covishield vaccine. Methods: Randomly selected health-care workers were followed up for SARS-CoV-2 immunoglobulin G (IgG) antibodies between 28 and 42 days after receiving their first vaccine dose. The VITROS SARS-CoV-2 IgG test (Ortho-Clinical Diagnostics, USA) with 100% specificity and > 90% sensitivity was used to assess seroconversion. Results: The first dose of vaccine induced seroconversion in 91.7% of beneficiaries. Nearly one-third (30.2%) of them had high antibody titers, and it showed a significant association with female gender (9.6 ± 5.5 vs. 7.6 ± 5.6) and younger age (P = 0.008). In addition, those with previous COVID infection showed a more robust immune response when compared to others (P = 0.001). Conclusion: Seroconversion rate of more than 90% offers a promising hope toward successful pandemic control. In the current scenario, the inability to attain the targeted coverage due to an upsurge in vaccine hesitancy, compounded with only lower proportion of seroconversion in elderly, faster rollout of the vaccines without any age limit, will help achieve the herd threshold more rapidly.