Characterizing Longitudinal Antibody Responses in Recovered Individuals Following COVID-19 Infection and Single-Dose Vaccination in British Columbia, Canada: a Prospective Cohort Study

BackgroundInvestigating antibody titres in individuals who have been both naturally infected with SARS-CoV-2 and vaccinated can provide insight into antibody dynamics and correlates of protection over time. MethodsHuman coronavirus (HCoV) IgG antibodies were measured longitudinally in a prospective cohort of PCR-confirmed, COVID-19 recovered individuals (k=57) in British Columbia pre- and post-vaccination. SARS-CoV-2 and endemic HCoV antibodies were measured in serum collected between Nov. 2020 and Sept. 2021 (n=341). Primary analysis used a linear mixed-effects model to understand the effect of single dose vaccination on antibody concentrations adjusting for biological sex, age, time from infection and vaccination. Secondary analysis investigated the cumulative incidence of high SARS-CoV-2 anti-spike IgG seroreactivity equal to or greater than 5.5 log10 AU/mL up to 105 days post-vaccination. No re-infections were detected in vaccinated participants, post-vaccination by qRT-PCR performed on self-collected nasopharyngeal specimens. ResultsBivariate analysis (complete data for 42 participants, 270 samples over 472 days) found SARS-CoV-2 spike and RBD antibodies increased 14-56 days post-vaccination (p<0.001) and vaccination prevented waning (B=1.66 [95%CI: 1.45-3.46]); while decline of nucleocapsid antibodies over time was observed (B=-0.24 [95%CI: -1.2-(-0.12)]). A non-significant trend towards higher spike antibodies against endemic beta-HCoVs was also noted. On average, SARS-CoV-2 anti-spike IgG concentration increased in participants who received one vaccine dose by 2.06 log10 AU/mL (95%CI: 1.45-3.46) adjusting for age, biological sex, and time. Cumulative incidence of high SARS-CoV-2 spike antibodies (>5.5 log10 AU/mL) was 83% greater in vaccinated compared to unvaccinated individuals. ConclusionsOur study confirms that vaccination post-SARS-CoV-2 infection provides multiple benefits, such as increasing anti-spike IgG titers and preventing decay up to 85 days post-vaccination.