Humoral Antibody Kinetics with ChAdOx1-nCOV (Covishield^TM) and BBV-152 (Covaxin^TM) Vaccine among Indian Healthcare workers: A 6-month Longitudinal Cross-sectional Coronavirus Vaccine-induced Antibody Titre (COVAT) Study

Background and Aims

There is limited data available on longitudinal humoral antibody dynamics following two doses of ChAdOx1-nCOV (Covishield^TM) and BBV-152 (Covaxin^TM) vaccine against SARS-CoV-2 among Indians.

Methods

We conducted a 6-month longitudinal study in vaccinated healthcare workers by serially measuring quantitative anti-spike antibody at 3-weeks, 3-months and 6- months after the completion of second dose. Geometric mean titer (GMT) and linear mixed models were used to assess the dynamics of antibody levels at 6 months.

Results

Of the 481 participants, GMT of anti-spike antibody decreased by 56% at 6- months regardless of demographics and comorbidities in 360 SARS-CoV-2 naive individuals, significantly in hypertensives. Participants with past infection had significantly higher GMT at all time points compared to naive individuals. Among SARS-CoV-2 naive cohorts, a significantly higher GMT was noted amongst the Covishield recipients at all time points, but there was a 44% decline in GMT at 6- month compared to peak titer period. Decline in GMT was insignificant (8%) in Covaxin recipients at 6-month despite a lower GMT at all time points vs. Covishield. There was 5.6-fold decrease in seropositivity rate at 6-month with both vaccines. Participants with type 2 diabetes mellitus have a lower seropositivity rate at all the time points. While seropositivity rate was significantly higher with Covishield vs. Covaxin at all time points except at 6-month where Covaxin recipients had a higher seropositivity, although no difference in seropositivity was noted in propensity-matched analysis.

Conclusions

There is waning humoral antibody response following two doses of either vaccine at six months.

Highlights:

• We assessed humoral antibody dynamics following two doses of the two vaccines used in India until 6 months.

• Our study of 481 health care workers showed a significant decrease in the anti-spike antibody at 6-months.

• Reduction in antibody was regardless of demographics, comorbidities and the vaccine type.

• T2DM cohorts had lowest seropositivity, while hypertensive had significant antibody decline at 6-month.