Safety and immunogenicity of SII-NVX-CoV2373 (COVID-19 vaccine) in adults in a phase 2/3, observer-blind, randomised, controlled study

Background NVX-CoV2373, a Covid-19 vaccine was developed in the USA with similar to 90% efficacy. The same vaccine is manufactured in India after technology transfer (called as SII-NVX-CoV2373), was evaluated in this phase 2/3 immuno-bridging study.Methods This was an observer-blind, randomised, phase 2/3 study in 1600 adults. In phase 2, 200 participants were randomized 3:1 to SII-NVX-CoV2373 or placebo. In phase 3, 1400 participants were randomized 3:1 to SII-NVX-CoV2373 or NVX-CoV2373 (940 safety cohort and 460 immunogenicity cohort). Two doses of study products (SII-NVX-CoV2373, NVX-CoV2373 or placebo) were given 3 weeks apart. Primary objectives were to demonstrate non-inferiority of SII-NVX-CoV2373 to NVX-CoV2373 in terms of geometric mean ELISA units (GMEU) ratio of anti -S IgG antibodies 14 days after the second dose (day 36) and to determine the incidence of causally related serious adverse events (SAEs) through 180 days after the first dose. Anti-S IgG response was assessed using an Enzyme -Linked Immunosorbent Assay (ELISA) and neutralizing antibodies (nAb) were assessed by a microneutralization assay using wild type SARS CoV-2 in participants from the immunogenicity cohort at baseline, day 22, day 36 and day 180. Cell mediated immune (CMI) response was assessed in a subset of 28 participants from immunogenicity cohort by ELISpot assay at baseline, day 36 and day 180. The total follow-up was for 6 months. Trial registration: CTRI/2021/02/ 031554.Findings Total 1596 participants (200 in Phase 2 and 1396 in Phase 3) received the first dose. SII-NVX-CoV2373 was found non-inferior to NVX-CoV2373 (anti-S IgG antibodies GMEU ratio 0.91; 95% CI: 0.79, 1.06). At day 36, there was more than 58-fold rise in anti-S IgG and nAb titers compared to baseline in both the groups. On day 180 visit, these antibody titers declined to levels slightly lower than those after the first dose (13-22 fold-rise above baseline). Incidence of unsolicited and solicited AEs was similar between the SII-NVX-CoV2373 and NVX-CoV2373 groups. No adverse event of special interest (AESI) was reported. No causally related SAE was reported.Interpretation SII-NVX-CoV2373 induced a non-inferior immune response compared to NVX-CoV2373 and has acceptable safety profile.