Background: SARS CoV 2 infection has severely ravaged health systems, economic and social progress globally in 2020. Seroprevalence studies can provide relevant information on the target populations for vaccination. They are relevant not only in the community, but also for critical population subgroups such as nursing homes or health care facilities. They will assist in strategizing the vaccination policy especially since there is limited availability of the vaccine and vaccine hesitancy Objective To evaluate the seroprevalence in Health Care Workers (HCW) at our hospital and to identify parameters which may affect it. Methodology: The Baseline profiling and seroprevalence of severe acute respiratory syndrome coronavirus 2 (SARS CoV 2) was assessed among 3258 healthcare workers (HCWs) of Medanta-The Medicity, Gurugram, Haryana, India, as a part of an ongoing cohort study.The fully automated LIAISON SARS CoV 2 S1/S2 IgG test using the chemiluminescence immunoassay (CLIA) for the quantitative determination of anti S1 and anti S2 specific IgG antibodies to SARS CoV 2 was used to test serum samples collected before the receipt of the vaccine. Seroprevalence was evaluated as per gender, age, association with previous Covid-19 diagnosis, use of supplements, and role in the hospital and type of exposure. Results: Of the 3258 participants tested for IgG serology (S1 and S2 proteins) 46.2% (CI 44.4 to 47.9%) were positive (i.e. had an antibody titre more than 15 Au/ml). Higher seroprevalence was seen in the others ie non clinical health care workers (including management, research personnel, pharmacists, technicians, general duty staff, housekeeping, security, food and beverage, and facility maintenance teams) (50.2 Au/ml) than that in clinical HCW (ie doctors and nurses)where it was significantly lower (41.4 Au/ml, p= 0.0001). Also, people with history of Covid-19 were found to have significantly higher antibody levels (p = 0.0001). Amongst the healthcare workers, doctors and nurses had higher relative risk of acquiring Covid-19 infection (RR = 1.21; 95% C.I.: 1.12 to 1.31). Conclusion: Seroprevalence in healthcare workers at our hospital is high at 46.2%. It is higher in non-clinical HCW than in clinical HCW . The risk of acquiring Covid 19 infection was higher in clinical HCW and thus, this subgroup may benefit most from vaccination. History of Covid 19 may provide double the protection, in particular in those who had it recently. Keywords: SARS CoV 2, vaccination, herd immunity, healthcare workers, seroprevalence

Background: The SARS-CoV-2 pandemic has severely impacted health systems, economic and social progress globally in 2020. The rollout of vaccines in several parts of the world is being hailed as a solution to the crisis. With newer and more virulent serotypes on the horizon and limited vaccine available, evaluation of safety and immunogenicity is critical for rationalization of vaccine use in public health. Objective To evaluate real world safety, and, immunogenicity of the Covishield vaccine, ChAdOx1 nCoV- 19 Corona Virus Vaccine (Recombinant) in Health Care Workers (HCW) during the national vaccine roll out in the NCR, New Delhi. The safety is evaluated through Adverse Events and Serious Adverse Events reported though enhanced pharmacovigilance protocols, and, the immunogenicity by quantitative determination of anti-S1 and anti-S2 specific IgG antibodies to SARS-CoV-2 in serum samples collected before the receipt of the vaccine and 14 days after dose 1, using the fully automated LIAISON SARS-CoV-2 S1/S2 IgG test using the chemiluminescence immunoassay (CLIA) Results: In the two weeks after immunization with the Covishield vaccine {ChAdOx1 nCoV- 19 Corona Virus Vaccine (Recombinant)}, none of the 1638 evaluated participants reported any serious adverse events (ie require hospitalization or emergency room visit). Solicited adverse events reported via daily diary cards included pain (62.7%) and soreness (24.1%) at injection site as most common, whereas fever (48.4%), headache (43.4%), myalgia (38.4%), fatigue (33.4%), joint pain (27.0%) and nausea (16.0%) were most common solicited systemic adverse events on day 1. Majority of local and systemic adverse events were seen in first 2 days post vaccination and thereafter they resolved. Lesser reactogenicity was observed in subjects with age >50 years. No major difference was observed in adverse events when subjects were stratified based on history of COVID 19 disease or baseline seropositivity. In our study serostatus improved from 48.2% positive at baseline to 79.0% positive 2 weeks following first dose of vaccination. After first dose of vaccination overall higher percentage (98.2%) of seropositivity rates were observed in those with past history of COVID 19 disease Conclusion: The Covishield vaccine {ChAdOx1 nCoV- 19 Corona Virus Vaccine (Recombinant)}, was safe and reported mild self limiting adverse events over 2-4 days and had an good early (within 2 weeks) seroresponse .This holds the promise of far reaching impact on vaccine availability for a larger population and thereby providing a widespread coverage.

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Background Seroprevalence studies on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection can provide information on the target populations for vaccination. We aimed to evaluate the seroprevalence among healthcare workers (HCWs) at our tertiary care institution and to identify parameters that may affect it. Method We assessed seroprevalence of SARS-CoV-2 by the chemiluminescence immunoassay test among 3258 HCW in our hospital and evaluated as per gender, age, their previous Covid-19 diagnosis, role in hospital and type/risk of exposure. Results Of 3258 participants, 46.2% (95% CI 44.4%– 47.9%) were positive for SARS-CoV-2 IgG antibodies (i.e. IgG ≥15 AU/ml). Higher seroprevalence was seen in non-clinical HCWs (50.2%) than in clinical HCWs (41.4%, p=0.0001). Furthermore, people with a history of Covid-19 were found to have significantly higher antibody levels (p=0.0001). Among the HCWs, doctors and nurses had lower relative risk (RR) of acquiring Covid-19 infection (RR=0.82; 95% CI 0.76–0.89) compared to non-clinical HCWs. Conclusion Seroprevalence in HCWs at our hospital was 46.2%. Clinical HCWs had lower seroprevalence compared to non-clinical HCWs. Previous history of Covid-19 almost doubled the seropositivity, particularly in those with current infection.

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