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Fifty five percent of the Pakistani population is still unvaccinated with the two-dose protocol of COVID-19 vaccines. This study was undertaken to determine the seroconversion rate and antibody titers following the two-dose BBIBP-CorV protocol, and to compare these variables in unvaccinated, COVID-19 recovered individuals (total n = 180) at Indus Hospital and Health Network, Karachi. Pseudotyped lentivirus antibody neutralization assays and SARS-CoV-2 IgG Quant II (Abbott) immunoassays were performed 4-8 weeks following the second dose of the BBIBP-CorV or PCR positivity/onset of symptoms of COVID-19. Seroconversion rate, using neutralization assays, in vaccinated individuals was lower (78%) than that in unvaccinated, COVID-19-recovered individuals with moderate to severe infection (97%). Prior PCR positivity increased serocoversion rate to 98% in vaccinated individuals. Immunoassays did not, however, reveal significant inter-group differences in seroconversion rates (≥95% in all groups). Log10 mean antibody neutralizing titers following the two-dose BBIBP-CorV protocol (IC50 = 2.21) were found to be significantly less than those succeeding moderate to severe COVID-19 (IC50 = 2.94). Prior SARS-CoV-2 positivity significantly increased post-vaccination antibody titers (IC50 = 2.82). Similar inter-group titer differences were obtained using the immunoassay. BBIBP-CorV post-vaccination titers may, thus, be lower than those following natural, moderate to severe infection, while prior SARS-CoV-2 exposure increases these titers to more closely approximate the latter.

ObjectivesTo compare the outcome of severe COVID-19 patients treated with Tocilizumab (TCZ). Methods: A retrospective cohort study comparing the clinical characteristics and outcomes of patients who received TCZ with those who did not, was conducted at The Indus Hospital, Karachi. A sub-group analysis was conducted on the TCZ group to identify predictors of mortality. Results 88 patients including 41 patients in the TCZ group and 47 in non-TCZ group were recruited. Baseline characteristics were comparable. TCZ group patients presented with worse clinical features including median SpO2 82% vs 88%, p<0.05 and CRP 193 vs 133.9 mg/L, p<0.05. TCZ group showed severe bilateral chest x-ray findings (92% vs 31%, p<0.05) compared to non-TCZ. In the TCZ group 85.4% were admitted in ICU compared to 69.8% in non-TCZ group, p>0.05. Mortality was not different among the groups (46% in TCZ group vs 51.1% in non-TCZ group, p>0.05). Median length of hospital stay, days of intubation, use of inotropic agents, use of invasive ventilation or in-hospital complications were not different between the groups. Sub-group analysis revealed that mortality within TCZ group was associated with high IL-6 levels (173 vs 69.66 pg/ml, p<0.05), ICU admission (100% vs 72%, p<0.05), need for mechanical ventilation (100% vs 13.6%, p<0.05) and higher incidence of in-hospital complications, p<0.05. ConclusionTCZ group had more critical patients and TCZ failed to demonstrate any mortality benefit in these patients. Non-survivors within the TCZ group were more critical compared to survivors and developed higher proportion of in hospital complications

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