A single dose ChAdOx1 nCoV-19 vaccine elicits high antibody responses in individuals with prior SARS-CoV-2 infection comparable to that of double dose vaccinated SARS-CoV-2 infection naïve individuals

Abstract

Background A 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 to those individuals. However, these important data are limited to developed nations and lacking in resource-limited countries, like Ethiopia. Methods We compared receptor-binding domain (RBD)-specific IgG antibodies in 40 SARS-CoV-2 naïve participants and 25 participants previously infected with SARS-CoV-2, who received two doses of ChAdOx1 nCoV-19 vaccine. We measured the antibody response in post-vaccination blood samples from both groups of participants collected at four different post-vaccination time points: 8- and 12-weeks after each dose of the vaccine administration using an in-house developed ELISA. Results We observed a high level of anti-RBD IgG antibodies titers 8-weeks after a single dose administration (16/27; 59.3%) among naïve participants, albeit dropped significantly (p<0.05) two months later, suggesting the protective immunity elicited by the first dose ChAdOx1 nCoV-19 vaccine will likely last for a minimum of three months. However, as expected, a significant (p<0.001) increase in the level of anti-RBD IgG antibodies titers was observed after the second dose administration in all naïve participants. By contrast, the ChAdOx1 nCoV-19 vaccine-induced anti-RBD IgG antibody titers produced by the P.I participants at 8- to 12-weeks post-single dose vaccination were found to be similar to the antibody titers seen after a two-dose vaccination course among infection- naïve participants and showed no significant (p>0.05) increment following the second dose administration. Conclusion Taken together, our findings show that a single ChAdOx1 nCoV-19 dose in previously SARS-CoV-2 infected individuals elicits similar antibody responses to that of double dose vaccinated naïve individuals. Age and sex were not associated with the level of vaccine-elicited immune responses in both individuals with and without prior SARS-CoV-2 infection. Further studies are required to assess the need for a booster dose to extend the duration and amplitude of the specific protective immune response in Ethiopia settings, especially following the Omicron pandemic.

Figure 1. Study design with the timeline for vaccination and sample collection. (b) Schematic representation of number participants at baseline and at four postvaccination time points.

Light red color character (Naïve) represents participants with SARS-CoV-2immunologically naïve and blue color (P.I.) represents participants with likely previous SARS-CoV-2 infection; BL =baseline or prevaccination; F1= 8-weeks after the first dose; F2=12-weeks after the first dose; F3 =8-weeks after the second dose; and F4 =8-weeks after the second dose. The first dose and second dose were given to participants at BL and F3, respectively prior to blood sample collection.

Figure 2. Analysis of ChAdOx1 nCoV-19 vaccine-induced antibody response in naïve and previously infected (P.I.) participants profile at different time points.

Comparison of anti-RBD IgG titers profile (a) between P.I. participants (red dots) before they received vaccination and convalescent serum panel (CSP: blue dotes); (b) between naïve (blue dots) and P.I. (red dots) participants across different time points before and after vaccination; among naïve participants (c) and (d)P. I. participants across different points. CSP=convalescent sera panel included as a reference to indirectly assess whether P.I. participants had previously either asymptomatic or symptomatic SARS-CoV-2 infection. Each colored dot corresponds to an individual participant. Horizontal bars represent mean with 95% CI of anti-RBD IgG titer levels (transformed to Log10 value) within the indicated groups. The broken line denotes the assay detection limit. Unpaired non-parametrical t-test with p <0.05 =*; p< 0.01=**; p<0.001=***; p<0.0001=****, ns=nonsignificant) was used compare the mean differences of anti-RBD IgG-antibodies titers across each time point of serum collection. BL=baseline or prevaccination; F1= 8-weeks after the first dose; F2=12-weeks after the first dose; F3 =8-weeks after the second dose; and F4 =8-weeks after the second dose. The first dose and second dose were given to participants at BL and F3, respectively prior to blood sample collection.

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). For panel C male vs female comparison was not done at F3 since there was infection naïve female participants that provided blood sample at F3.