Fig. 3: Comparison of antibody titre, pseudovirus neutralisation and inhibition capacity in individuals with and without prior evidence of SARS-CoV-2 infection in an older-adult two-dose vaccinated population.

Centre line: median; box limits: first and third quartile; whiskers: 1.5*IQR; points: outliers. Anti-RBD anti-receptor binding domain antibody as measured by double antigen-binding assay. Results sampling post-second dose vaccine stratified by those with no evidence of prior infection (brown), evidence of asymptomatic infection (green) and symptomatic infection (blue). a n = 192 individual participants. Those with asymptomatic infection saw a 7.5-fold (95% CI 4.6–12.1) increase in Abbott IgG CMIA antibody titres, while those with prior symptomatic infection saw a 20.3-fold (95% CI 9.7–42.5) increase. Data from this study provide strong evidence for these associations in this age group (LRT on Tobit model, p < 0.000001). b n = 184 individual participants. There is very strong evidence for an association between pre-vaccination SARS-CoV-2 exposure and higher neutralisation percentage at time point three (post-second dose vaccine [p < 0.0001]), c n = 182 individual participants. The RBD DABA titre at 4 months post first dose (i.e. 2 weeks after the second dose) is likely to be higher in those who had symptomatic Covid-19 prior to vaccination (95% CI 0.97–1.7; point estimate 1.27) and it is 1.29 times higher in those who only had prior seropositivity (95% CI 1.1–1.6), when compared to those who did not have Covid-19 or seropositivity. Data from this study provide some statistical evidence for these associations (LRT p = 0.03). d n = 183 individual participants. There is very strong evidence for an association between pre-vaccination SARS-CoV-2 exposure and higher RBD antibody-binding inhibition percentage at time point three (p < 0.0001).