Dynamics of Antibody Response to Covishield Vaccine after 6 Months: A Longitudinal Prospective Study.

OBJECTIVES: To study the dynamics of antibody responses in the real world up to 6 months following two Covishield vaccination doses and evaluate its correlation with age. MATERIALS AND METHODS: From March 2021 to February 2022, a prospective, longitudinal study of healthcare workers (HCWs) from a dedicated COVID-19 hospital was conducted. Institutional Ethics Committee permission was obtained. HCWs were divided into two groups. The first group consisted of individuals who had received the first dose of the COVID-19 vaccine, with at least 3 weeks elapsed since the dose, and who had not received the second dose until the initial blood sample for antibody testing was obtained. The second group consisted of individuals who had received both COVID-19 doses and had at least 2 weeks between the administration of the second dose and the collection of the first sample for antibody testing. In March 2021, after undergoing phlebotomy for serum collection, the participants responded to the survey. Electrochemiluminescence immunoassay (ECLIA) was used to perform a quantitative test for antibodies to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (S) protein receptor domain [receptor binding domain (RBD)]. The test used had a 98.8% sensitivity and a 99.9% specificity. If the antibody titer was 0.80 U/mL or higher, it was deemed positive; if it was lower, it was deemed negative. Two follow-ups were conducted for both groups, 3 and 6 months following the first sample collection. During both follow-up visits, a blood sample was obtained for testing the amount of antibody response, and the history of COVID-19 disease following the initial sample was taken. RESULTS: Every HCW had received the Covishield vaccination. After the vaccine's first dosage, 61 HCWs in the first group underwent antibody testing. The information about the 43 HCWs in the first group who attended the two follow-ups is as follows. There were 14 (32.6%) nurses and 5 (11.6%) doctors among the 43 HCWs. The age range was 21-55 years, with the median [interquartile range (IQR)] age being 26 (22-40) years and 20 (60.5%) being females. The vaccination series had a median (IQR) of 34 (29-49) days between doses. There was a statistically significant difference in immunoglobulin G (IgG) levels of the three samples, χ2 = 13.579, p = 0.001. Median (IQR) IgG levels of the three samples at 1 month after the first dose, 3 and 6 months after the second dose were 8511 (51-15400) U/mL, 1471 (249-5050) U/mL, and 978 (220-2854) U/mL, respectively. The antibody titer was negative for two HCWs in the first sample, positive in the rest of the samples, and positive in all samples in both follow-ups. In the second group, following two COVID-19 dosages, a total of 65 HCWs had tested positive for antibodies. The information of the 56 HCWs in group II who attended both follow-ups is as follows. Of the 56 HCWs, 15 (26.8%) were doctors, 27 (48.2%) were nurses, and 14 (25%) were others. The age range was 20-64 years, with a median (IQR) of 29.5 (22-37.7) and 31 (55.3%) female participants. The vaccination series had a median (IQR) interval of 32 (29-35) days between doses. There was a statistically significant difference in IgG levels of the three samples, χ2 = 31.107, p < 0.0001. Median (IQR) IgG levels of the three samples at 20 days, 3.8 months, and 7 months after the second dose were 2377.5, 1345.5, and 1257 U/mL, respectively. Spearman's rank order correlation was used to assess the association between IgG level and age in both groups. The relationship between IgG levels and age was weakly correlated and not statistically significant. CONCLUSION: There is a waning of antibody titer over time postimmunization. A lower antibody titer can be a contributing factor for infections that emerge later. IgG levels postvaccination do not differ according to age.

SARS-CoV-2 Antibody Response Following COVID-19 Vaccination, a Longitudinal Study.

Background: The objective was studying the antibody response following immunization with COVID-19 vaccines. Material and Methods: It was a longitudinal study of healthcare workers (HCWs). Two groups were taken, Group 1 had taken first dose of the COVID-19 vaccine, at least 3 weeks have passed. Group 2 had taken two doses of COVID-19 vaccine and at least 2 weeks have passed. A quantitative test for antibodies to SARS-CoV-2 spike protein was done. Follow-up of both groups was done after 3 months of collection of the first sample. Results: The antibody titre of the 57 HCWs in Group 1, decreased significantly 125 days after the first dose [median = 2,013 U/ml] as compared to the titre 30 days after the first dose of Covishield vaccine[median = 9,965.26 U/ml]. The median interval between two doses of vaccine was 34 days. In Group 2, the antibody titre of the 60 HCWs in Group 2, decreased significantly 114 days after second dose[median = 1,411 U/ml] as compared to the titre 19.5 days after second dose of Covishield vaccine [median = 2,377.5]. There was no significant difference in the antibody titre in follow-up samples of HCWs with and without side effects. Conclusion: The antibody titre decreases after 13 to 17 weeks post the second dose of Covishield vaccination. The decision of the Government of India to increase the interval between two doses of Covishield is justified. Low antibody titre can be the reason for breakthrough infections. The antibody titre was not related to side effects post-vaccination.

Assessment of Risk Factors for COVID-19 in Health Care Workers: A Nested Case-Control Study.

OBJECTIVES: To study the risk factors for SARS-CoV-2 infection in health care workers (HCWs) exposed to COVID-19 patients. MATERIAL AND METHODS: This was a nested case-control study of health care workers(HCWs) in a Dedicated COVID Hospital(DCH). The data collection was done from Dec 2020 to Feb 2021. The study was part of an international multicenter study by the World Health Organisation (WHO).2 The Doctors, nurses, housekeeping staff, clerks, and other staff working in this DCH were considered as HCWs. HCWs working in this DCH with confirmed COVID-19 were recruited as cases and other HCWs working in this DCH in the same Ward/ICU/office without infection were recruited as controls (incidence density sampling). Three controls were taken per case. The questions were in the Likert scale. RESULTS: There were 25 cases and their 75 controls. There was no significant difference between cases and controls with respect to age, sex, occupation, education, and comorbidities and all controls were negative for antibodies at the time of the interview. Most (70%) of the HCWs were doctor by profession followed by nurses (19%). All HCWs were trained in IPC (infection Prevention and Control). Most (96%) HCWs reported that PPE (personal protective equipment) is available in sufficient quantity. There was no significant difference between cases and controls with respect to those having direct contact with the patient's materials, surroundings, and following hand hygiene. CONCLUSION: Adequate availability of PPE, IPC training of HCWs are important for preventing COVID-19 but do not completely reduce risk among HCWs.