3.3.1. 18–60 Age Cohort
Immunogenicity assessment in the 18–60 age cohort was performed during Stage 3 on 122 participants of the Vaccine Group and in 45 participants of the Placebo Group. Due to the lack of defined correlates of protection against COVID-19 and the low correlation between seropositivity rates assessed in NT and CMIA at all time points (Immunogenicity assessment was also performed separately both for the participants who were anti-SARS-CoV-2 nAB negative (69/122 in Vaccine Group and 28/45 in Placebo Group) or anti-SARS-CoV-2 nAB positive (53/122 in Vaccine Group and 17/45 in Placebo Group) at screening.Participants with undetectable anti-SARS-CoV-2 antibodies at screening (with any method) showed increasing nAB titers and seroconversion from day 7 post 1st vaccination (According to the protocol of the clinical trial, seroconversion for participants who had detectable SARS-CoV-2 nABs at screening was defined as 4-fold increase in nAB titers after vaccination compared to baseline titers.Participants who had detectable antibodies against SARS-CoV-2 at screening showed increased nAB titers at days 7 and 14 post 1st vaccination. However, after the 2nd vaccination the titers did not increase significantly (