ABSTRACT
Background: The change in serological status of community may be used as input for guiding the public health policy. Hence, the present study was conducted to determine change in seroprevalence of COVID-19 among healthcare workers (HCWs). Methods: From the baseline multicentric study sample, a subsample was followed up, and a seroepidemiological study was conducted among them between 6 and 22 weeks after the second dose of the vaccination. Multistage population proportion to size sampling was performed for the selection of subsample of HCWs. The serosurvey was conducted using the enzyme-linked immunosorbent assay-based IgG antibody test (COVID KAVACH). Results: Follow-up serological testing was done in subsample of 1122 participants of original 3253 participants. The mean age of the participants was 34.6 (8.13) years. A total of 300 (26.7%) participants were females. The seroprevalence was 78.52, (95%CI:76-80.1). Among those who were seronegative at initial test, 708 (77.04%) were seroconverted. Those who were not seroconverted (241 (21.5%)) have longer duration from the second dose of the vaccination (93 (31.4) vs. 56 (38.4); p value < 0.001). The COVID-19 infection was significantly associated with seropositive status and being a medical staff was associated with remaining seronegative on follow-up. The higher age (≥50 years) was found to be significantly associated with seroreversion. Conclusion: Four in five HCWs had detectable antibodies. Seroepidemiological studies carry vital information to control the public health response in the course of the pandemic. The study can also further help as a platform to study the seroconversion and effect of vaccination among HCWs for newer variants of SARS-CoV-2.
ABSTRACT
Background: Despite having an effective COVID-19 vaccine, the COVID-19 pandemic is far from over and the delta variant continues to cause havoc across several continents. The present study was conducted to analyze and describe the occurrence of COVID-19 cases among completely vaccinated individuals. Methods: In an educational institute in Western Maharashtra, we analyzed a cluster of RTPCR positive COVID-19 cases among fully vaccinated students which occurred in 12 days. The cases were linked to a series of curricular and co-curricular events in the institute. A detailed epidemiological investigation and genome sequencing of cases were conducted. IgG antibodies against S1 protein of novel SARS-CoV-2 were estimated for cases and age, sex, and vaccination status matched controls. Results: All 37 identified cases were mild COVID. 188 high risk (HR) contacts of the cases were identified. The overall secondary attack was 9.5%. Out of 31 cases and 50 controls, 09 (29%) cases and 08 (16%) controls were found to have IgG antibodies against S1 protein of novel SARS-CoV-2 titer of more than 60 U/ml. Whole-genome sequencing of 15 samples of the cluster showed the presence of the Delta variant of SARS-CoV-2. No correlation was observed between Ct value and IgG S1 antibody titers. Conclusion: The study provides significant evidence that only vaccination alone does not completely protect against SARS-CoV-2 B.1.617.2 (Delta) variant infection. An all-encompassing multicomponent strategy involving implementation of NPIs, robust contact tracing, early identification and isolation of cases, and high vaccination coverage is the way forward for the prevention of COVID-19.
ABSTRACT
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.