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Background The immune response after SARS-CoV-2 is complex and may be affected by severity of the disease, race, etc. The present study was conducted to assess the serial antibody response among the COVID-19 patients admitted in the hospital. Methods The study was conducted between July and October 2020 in a dedicated COVID-19 hospital. All consented patients underwent serial testing of antibodies using a rapid chromatographic immunoassay-based qualitative IgG/IgM kit every third day until their discharge or death. The data about age, sex, severity of disease, length of stay, onset of symptoms, date of molecular testing were also collected. Appropriate statistical tests were used. Results The mean age of 1000 COVID-19 patients was 47.5 ± 17.9 years. Out of the total, 687 (68.7%) were males. With respect to severity, 682 (68.2%) were asymptomatic/mild, 200 (20%) were moderate and 118 (11.8%) were severe cases. The seroconversion percentage increased from 12.8% to 97.9% and 16.3% to 80.9% for IgG and IgM respectively in 21 days. The median time for seroconversion was 10 days (IQR:6–12 days) for IgG and eight days (IQR: 6–11 days) for IgM. At the time of discharge (median nine days), detectable IgG and IgM antibodies were present in 502 (52.46%) and 414 (43.26%) participants respectively. Seroconversion was associated with days after the symptoms, increasing severity of the disease and the presence of co-morbidity. Conclusion Seroconversion increased during the period of observation. The severe/moderate cases of COVID-19 tend to have an early seroconversion as compared to the asymptomatic/mild cases. Only half of the patients were seroconverted at discharge.

Background The first dose of the ChAdOx1 nCoV- 19 Corona Virus Vaccine (Covishield) was administered to the eligible beneficiaries of tertiary care institute of Western Maharashtra on 16 Jan 21 and in the past three months almost 97% of the staff has been vaccinated. The present study analyses the incidence of COVID cases in the unvaccinated and vaccinated population of the institute. Methods All Covid 19 infections (RT-PCR positive) from 01 February 21 to 25 April 21 were included in the study and analyzed as per their vaccination status. To assess the COVID 19 transmission in contacts, Secondary Attack Rates (SAR) of the pre-vaccination period (Jun–Oct 20) was compared with the present SAR. Results A total of 113 cases occurred in the study period (01 Feb to 25 Apr 21). Lower number of infections were observed among the fully vaccinated as compared to partially vaccinated and non-vaccinated. The overall vaccine effectiveness was found to be 88.6% (81.55–92.37) and 44.1% (4.55–67.3) in completely and partially vaccinated individuals respectively. Hazard Ratios for getting infected dropped significantly after 28 days of the second dose. The SAR in high risk contacts (HRCs) was found to be 4.25%, which was lower than SAR (20.6%) of pre-vaccination period. Conclusion This is one of the earliest studies in India to report the impact of COVID-19 vaccination. The results indicate that the vaccine provides effective protection against COVID-19 infection. However, given the complex dynamics of vaccination, the role of NPIs and implementation of COVID appropriate behavior cannot be undermined.

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