High seroconversion rates persist up to 6 months post-vaccination.
Seroconversion rates were examined on Day 14, Day 28 and Month 6 post-vaccination measured from participants in the Ad5-nCoV (n = 371) or the Placebo group (n = 124; from the FAS for immunogenicity analysis). The seroconversion rates with 95% CI (calculated using the Clopper-Pearson method) are shown for serum antibodies against Next, pre-existing anti-Ad5 neutralising antibody titres were examined between participants in the Ad5-nCoV and Placebo groups at Day 0, Day 28 and Month 6 post-vaccination. Almost all participants had neutralising antibodies against the Ad5 vector at baseline: 317/371 (85.5%) participants who received Ad5-nCoV and 106/124 (85.5%) who received placebo. Of the total participants with pre-existing anti-Ad5 titres at Day 0 (n = 423), most participants had low Ad5 antibody titres (≤1:200), whereas only seven participants (1.7%) with pre-existing anti-Ad5 antibodies had high levels (>1:200). Of those in the Ad5-nCoV group, GMTs of anti-Ad5 participants with low pre-existing anti-Ad5 antibodies increased from 11.3 at baseline (n = 317) to 36.5 at Day 28 (n = 353), which then increased further to 48.3 (n = 355) at Month 6. Corresponding values for the very few participants with pre-existing immunity to Ad5 >1:200 showed an increase from 320.0 at baseline (n = 6) to 359.2 at Day 28 (n = 6) and a further increase to 557.2 at Month 6 (n = 6).As illustrated in 