Background
Due to waning immunity following primary immunization with Covid-19 vaccines, booster doses may be required. The present study assessed a heterologous booster of SII-NVX-CoV2373 (spike protein vaccine) in adults primed with viral vector and inactivated vaccines.
Methods
In this Phase 3, observer-blind, randomized, active controlled study, a total of 372 adults primed with ChAdOx1 nCoV-19 (n = 186) or BBV152 (n = 186) at least six months ago, were randomized to receive a booster of SII-NVX-CoV2373 or control vaccine. The control group received homologous booster of ChAdOx1 nCoV-19 or BBV152 depending upon the prime cohort. Anti-S IgG and neutralizing antibodies were assessed at baseline (day 1), day 29, day 91 and day 181 for immunogenicity assessments. Solicited reactions were collected for one week after vaccination. Unsolicited adverse events (AEs) were collected for 28 days while serious adverse events (SAE) and adverse events of special interest (AESI) were reported throughout the six-month study duration. (Identifier: CTRI/2022/04/042017)
Results
In both the ChAdOx1 nCoV-19 primed group and BBV152 primed group, 186 participants each received the study vaccines. In the ChAdOx1 nCoV-19 Prime cohort, at 28 days after the booster dose, there was a 3.9- to 5.1-fold-rise and 1.9- to 2.8-fold-rise in anti-S IgG and neutralizing antibody titres from the baseline in the SII-NVX-CoV2373 group and the ChAdOx1 nCoV-19 group, respectively. The same responses for the BBV152 prime cohort was 7.4- to 10.4-fold-rise and 1.5- to 2.5-fold-rise in the SII-NVX-CoV2373 group and the BBV152 group, respectively. There was 86.96% (95% CI 78.32, 93.07) to 94.57% (95% CI 87.77, 98.21) and 37.63% (95% CI 27.79, 48.28) to 79.57% (95% CI 69.95, 87.23) anti-S IgG and neutralizing antibody seroresponse (2-fold-rise from baseline) in the SII-NVX-CoV2373 group and ChAdOx1 nCoV-19 group, respectively. The same was 94.51% (95% CI 87.64, 98.19) to 98.90% (95% CI 94.03, 99.97) and 20.43% (95% CI 12.77, 30.05) to 74.19% (95% CI 64.08, 82.71) in the SII-NVX-CoV2373 group and BBV152 group, respectively. No SAE or AESI was caused by the study vaccines.
Conclusion
SII-NVX-CoV2373 showed a numerically higher boosting effect than homologous boosters in adults primed with ChAdOx1 nCoV-19 and BBV152. The vaccine was also safe and well tolerated.