Covishield vaccine induces robust immune responses in Bangladeshi adults.

OBJECTIVE

To evaluate severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2)-specific antibody responses after Covishield vaccination for 6 months after vaccination.

DESIGN

SARS-CoV-2-specific antibody responses were assessed by enzyme-linked immunosorbent assay of the recombinant receptor-binding domain of SARS-CoV-2 in 381 adults given the Covishield vaccine at baseline (=119), 1 month (=126) and 2 months (=75) after the first dose, 1 month after the second dose (=161), and monthly for 3 additional months.

RESULTS

Over 51% of participants were seropositive at baseline (before vaccination with Covishield), and almost all participants (159/161) became seropositive 1 month after the second dose. Antibody levels peaked 1 month after receipt of the second dose of vaccine, and decreased by 4 months after the first dose; the lowest responses were found 6 months after the first dose, although antibody responses and responder frequencies remained significantly higher compared with baseline (<0.0001). Compared with younger participants, older participants had lower antibody responses 6 months after the first dose of vaccine (<0.05). Participants who had previous SARS-CoV-2 infection showed robust higher antibody responses after vaccination.

CONCLUSIONS

These findings help to elucidate the longevity of vaccine-specific antibody responses following vaccination with Covishield, and provide information relevant to the planning of booster doses after the initial two doses of vaccine.