A collaborative study published on the preprint server bioRxiv* demonstrates that antibodies generated in response to messenger ribonucleic acid (mRNA)-based coronavirus disease 2019 (COVID-19) vaccination target more epitopes across the viral spike protein as compared to that targeted by infection-induced antibodies.
Study: Comprehensive characterization of the antibody responses to SARS-CoV-2 Spike protein after infection and/or vaccination. Image Credit: Kateryna Kon / Shutterstock.com
The combination of mass vaccination with non-pharmaceutical control measures like mask-wearing and physical distancing is the best possible way to bring an end to the COVID-19 pandemic. Multiple potential vaccines are currently rolling out in many countries across the globe. In the United States, more than 50% of the adult population have already been vaccinated mostly by either of the two mRNA-based COVID-19 vaccines, BNT162b2 (Pfizer/BioNTech) and mRNA-1273 (Moderna).
Several studies have highlighted the potency of these vaccines in preventing the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, severe disease, and mortality. However, it is still uncertain whether these vaccines can retain their antiviral efficacy against newly emerging variants of SARS-CoV-2.
Studies on endemic coronaviruses have shown that continuous evolution of the spike protein through mutations can facilitate the virus escape from neutralizing antibodies induced by natural infection. Similarly, some recent studies have shown that the SARS-CoV-2 Delta variant can induce breakthrough infections in fully vaccinated individuals, thus highlighting the possibility of emerging escape mutations. Routine monitoring of vaccine efficacy is thus important to better manage the pandemic.
In the current study, the scientists have characterized the dynamics of antibody response induced by mRNA COVID-19 vaccination or natural SARS-CoV-2 infection.
The scientists used phage peptide libraries and deep mutational scanning (phage-DMS) to identify spike-specific epitopes and escape sites for antibodies induced by vaccination, infection, or both. To identify potential escape mutations within the epitope regions, antibody binding of wild-type peptides was compared to that of mutated peptides.
The analysis was conducted using serum samples obtained from mRNA-1273-vaccinated, BNT162b2-vaccinated, or SARS-CoV-2-infected individuals, as well as, from vaccinated individuals with a history of COVID-19.
The findings revealed that the most commonly targeted epitopes across the study population include N-terminal and C-terminal domains (NTD and CTD, respectively) in the spike S1 subunit, as well as fusion peptide and heptad-repeat regions in the spike S2 subunit.
More specifically, fusion peptide and heptad-repeat regions appear to be the most frequently targeted epitopes in mildly infected, unvaccinated individuals. In contrast, antibodies generated in response to vaccination or severe infection target all four epitopes identified. Interestingly, antibodies obtained from infection- and vaccination-naïve individuals showed occasional cross-reactivity to fusion peptide and heptad-repeat regions, thereby indicating that these epitopes are conserved between SARS-CoV-2 and endemic coronaviruses.
Antibodies generated in response to mild infection showed significantly higher binding to the fusion peptide. In contrast, vaccination- or severe infection-induced antibodies showed significantly higher binding to NTD, CTD, and heptad-repeat regions.
The study did not observe any significant impact of age, vaccine dosage, vaccine type, and timepoint since the last vaccination/symptom onset on the epitope binding efficiency of antibodies.
Sites of escape within epitopes
NTD and CTD
The analysis of spike-specific mutations responsible for antibody escape revealed that the majority of vaccine-induced antibodies are highly sensitive to mutations located at the extreme C-terminal portion of the NTD and the region located between NTD and spike receptor-binding domain (RBD).
The N-terminal portion of the CTD was identified as the most dominant epitope for vaccine-induced antibodies. Within this epitope, two sites were identified as potential escape sites in most of the samples.
The unique escape profile induced by vaccination across individuals appeared to change over time.
Antibodies induced by both infection and vaccination showed sensitivity to four sites within the fusion peptide epitope. However, in infected individuals, no change in escape profile was observed after vaccination.
In infection-naïve individuals, vaccination-induced distinct escape profiles within the fusion peptide epitope.
Distinct escape profiles were identified within the heptad-repeat region epitope in previously infected, unvaccinated individuals. In contrast, a unique escape profile was identified in vaccinated individuals with or without previous infection.
The current study identifies four major epitopes outside the spike RBD that are targeted by vaccination- and severe infection-induced antibodies. However, antibodies induced by mild infection targets only two of these epitopes. This indicates that COVID-19 vaccination induces a comparatively broader antibody response than natural infection.
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.