ABSTRACT
Background: A recombinant, adjuvanted COVID-19 vaccine, SII-NVX-CoV2373 was manufactured in India and evaluated in Indian children and adolescents to assess safety and immunogenicity. Methods: This was a Phase 2/3 observer-blind, randomized, controlled study in children and adolescents aged 2 to 17 years. Participants were randomly assigned in 3:1 ratio to receive two doses of SII-NVX-CoV2373 or placebo on day 1 and day 22. Solicited adverse events (AEs) were collected for 7 days after each vaccination. Unsolicited AEs were collected for 35 days following first dose and serious AEs (SAEs) and adverse events of special interest (AESI) were collected throughout the study. Anti S IgG and neutralizing antibodies against the SARS-CoV-2 were measured at baseline, day 22, day 36 and day 180. Variant immune responses were assessed in a subset of participants at baseline, day 36 and day 180. Primary objectives were to demonstrate non-inferiority of SII-NVX-CoV2373 in each pediatric age group (12 to 17 years and 2 to 11 years, separately) to that in adults in terms of ratio of titers of both anti-S IgG and neutralizing antibodies 14 days after the second dose (day 36). Non-inferiority was to be concluded if the lower bound of 95% CI of the ratio was >0.67. Results: A total of 920 children and adolescents (460 in each age cohort; 12 to 17 years and 2 to 11 years) were randomized and vaccinated. The demographic and baseline characteristics between the two groups were comparable in both age groups. After the second dose, there were more than 100-fold rise in anti-S IgG GMEUs and more than 84-fold rise in neutralizing antibodies GMTs from baseline in the participants who received SII-NVX-CoV2373. The GMTs in both age groups were non-inferior to those observed in Indian adults. The seroconversion rate was [≥] 98% (anti-S IgG) and [≥] 97.9% (neutralizing antibodies) in both age groups, respectively. Similar findings were seen in the baseline seronegative participants. SII-NVX-CoV2373 also showed robust responses against various variants of concern. Injection site pain, tenderness, swelling, erythema and fever, headache, malaise, fatigue, myalgia, arthralgia, nausea and vomiting were the common solicited adverse events which were transient and resolved without any sequelae. Throughout the study, only two causally unrelated SAEs and no AESI were reported. Conclusion: SII-NVX-CoV2373 has been found safe and well tolerated in children and adolescents of 2 to 17 years. The vaccine was highly immunogenic and the immune response was non-inferior to that in adults.