A Single Dose of ChAdOx1 nCoV-19 Vaccine Elicits High Antibody Responses in Individuals with Prior SARS-CoV-2 Infection Comparable to That of Two-Dose-Vaccinated, SARS-CoV-2-Infection-Naïve Individuals: A Longitudinal Study in Ethiopian Health Workers

Abstract

Single-dose COVID-19 vaccines, mostly mRNA-based vaccines, are shown to induce robust antibody responses in individuals who were previously infected with SARS-CoV-2, suggesting the sufficiency of a single dose for those individuals in countries with limited vaccine supply. However, these important data are limited to developed nations. We conducted a prospective longitudinal study among Ethiopian healthcare workers who received a ChAdOx1 nCoV-19 vaccine. We compared the geometric mean titers (GMTs) of the SARS-CoV-2 receptor-binding domain (RBD)-specific IgG antibodies in 39 SARS-CoV-2 naïve participants and 24 participants previously infected with SARS-CoV-2 (P.I.), who received two doses of ChAdOx1 nCoV-19 vaccine across the two post-vaccination time points (at 8 to 12 weeks post single dose and two dose vaccinations). We noted that the GMT (1632.16) in naïve participants at 8-12 weeks post first dose were comparable to the GMT (1674.94) observed in P.I. participants prior to vaccination. Interestingly, P.I. participants had significantly higher antibody titers compared to naïve participants, after both the first (GMT, 4913.50 vs. 1632.16) and second doses (GMT, 9804.60 vs. 6607.30). Taken together, our findings show that a single ChAdOx1 nCoV-19 dose in previously SARS-CoV-2 infected individuals elicits similar, if not higher, antibody responses to those of two-dose-vaccinated naïve individuals.

Keywords: ChAdOx1 nCoV-19; RBD; SARS-CoV-2; dose; naïve; prior infection; vaccine.

Figure 1

Cohort study design showing the ChAdOx1 nCoV-19 vaccine vaccination regimes and serum sample collection time points: (A) Study design with a timeline for vaccination and blood sample collection. (B) Schematic representation of the number of participants enrolled at prevaccination and two post-vaccination time points. The first dose and second dose were given to participants prior to the two-time points for blood sample collection. Light red characters (Naïve) represent participants immunologically naïve to SARS-CoV-2 and blue characters (P.I.) represent participants with likely previous SARS-CoV-2 infection. Pre Vacc = baseline or prevaccination; 1d + 8–12w= 8–12 weeks after the first dose; 2d + 8–12w = 8–12 weeks after the second dose.

Figure 2

Analysis of the ChAdOx1 nCoV-19 vaccine-induced antibody response in naïve and previously infected (P.I.) participants profile at different time points. Comparison of mean log10 anti-RBD IgG titers between naïve (A) and P.I. (B) participants across different time points before and after vaccination. Horizontal bars represent the means with 95% CIs of anti-RBD IgG titer levels (transformed to Log10 value) within the indicated groups. The broken line denotes the assay detection limit. Unpaired and non-parametrical Mann–Whitney test was used to compare the mean differences in log10 anti-RBD IgG titers for each time point of serum collection. A p-value <0.05 was considered statistically significant, and p >0.05 was considered non-significant (ns). Pre Vacc = baseline or prevaccination; 1d + 8–12w = 8–12 weeks after the first dose; 2d + 8–12w = 8–12 weeks after the second dose.

Figure 3

Antibody response by age and sex of naïve and previously infected (P.I.) participants following vaccination. Antibody response comparison of (A) naïve and (B) P.I. participants by age: 40–59 (blue dots) versus 21–39 years (red dots); antibody response comparison of (C) naïve and (D) P.I. participants by sex: male (blue dots) versus female (red dots). Pre Vacc = baseline or prevaccination; 1d + 8–12w = 8–12 weeks after the first dose; 2d + 8–12w = 8–12 weeks after the second dose. Unpaired and non-parametrical Mann–Whitney test was used to compare the mean differences in log10 anti-RBD IgG-antibodies titers at each time point of serum collection. A p-value <0.05 was considered statistically significant, and p > 0.05 was considered non-significant (ns).