Thread by @NavroopSingh_

Antibody Response after Second-dose of ChAdOx1-nCOV (CovishieldTM) and BBV-152 (CovaxinTM) among Health Care Workers in India: Final Results of Cross-sectional Coronavirus Vaccine-induced Antibody Titre (COVAT) study - medrxiv.org/content/10.110…

this cross-sectional COVAT study reported an overall 95.0% (489/515) seropositivity rate after the two complete doses of both vaccines in entire cohorts that include both SARS-CoV-2 naïve and recovered individuals (Covishield 98.1% and Covaxin 80.0%, respectively).

While seropositivity rates after two complete doses was 97.8% and 79.3% with Covishield and Covaxin, respectively in SARS- CoV-2 naïve individuals; 100% of cohorts with a past history of SARS-CoV-2 were seropositive after the two doses of both vaccines.

Notably, while both vaccines showed an increase in seropositivity and median (IQR) anti-spike antibody titre after the second dose, Covaxin gained a significant increase in both seropositivity and antibody titre only after the two completed doses.

Contrarily, Covishield showed a
good seropositivity rate and a 4-fold rise in median antibody titre even after a single dose. One dose of either vaccine yielded a very high seropositivity and anti-spike antibody titre in SARS-CoV-2 recovered individuals.

However, we also acknowledge several limitations. Firstly, in the present study, we have used a convenience sampling amounting to selection bias. A community-based study in a larger population with multi-stage sampling would be an ideal sampling method.

Thirdly, we have measured only anti-spike binding antibody and could not assess NAb and cell-mediated immune response such as Th-1 and Th-2 dependent antibody or cytokines (primarily due to the lack of standardized commercial labs in Indi

Fourth, we could not measure the baseline anti-spike antibody titre prior to the vaccination, because of logistic issue due to lockdown.

Finally, two value of short-term anti-spike antibody as evaluated in this report may not necessarily predict the efficacy of vaccine, nor the absence of seropositivity confer failure of vaccine in absence of NAb and T-cell response assessment.

In conclusion, this cross-sectional study after the completion of two doses of both vaccines suggests that both vaccines induce seropositivity to anti-spike antigen in 95% of SARS-COV-2 naïve and recovered individuals after 3-weeks.

Whether any real difference in inducing immunogenicity exists between two vaccines can only be meaningfully demonstrated through a head-to-head RCT.

In sum & substance in this study on HCW, COVIDSHIELD Showed little better response on Spike Protein & hAB response compared to COVAXIN but with second dose COVAXIN matched the response. Also study takes response to spike protein only not asses Anti Bodies or Cell immune response.

COVAXIN is based on Inactivated Virus platform induced Th1 based response due to the use of Algel-IMDG (chemosorbed imidazoquinoline onto the aluminum hydroxide gel) as an adjuvant leading to longer & better T/B Cell immunity and response in case of an infection - As per BB !

Also while COVAXIN inactivated virus deals with M, N & E Protein of Virus along with Spike Protein. Adenovirals like COVIDSHIELD induce human cells to generate Response to Spike Protein particularly. This is a difference of how two works.

Also this study doesnt mention the against which STRAIN of SARS COV were the study conducted. Also it has many caveats. So for Delta Strain B.1.617.2 refer other studies like of Lancet to understand efficacy of COVIDSHIELD & Pfizer against mutant strains.