# Hybrid Immunity in a Mozambican Cohort After 1 or 2 Doses of the BBIBP-CorV Vaccine

## TL;DR

A single dose of the BBIBP-CorV vaccine in people previously exposed to SARS-CoV-2 provides stronger antibody responses than two doses in those who were not previously exposed.

## Contribution

This study is the first to show that prior SARS-CoV-2 exposure enhances the immune response to the BBIBP-CorV vaccine in a Mozambican cohort.

## Key findings

- Seropositive individuals had higher antibody titers and neutralizing activity after one dose compared to seronegative individuals after two doses.
- A second dose of the BBIBP-CorV vaccine did not significantly boost antibody responses in those already seropositive.
- Antibody-dependent cellular cytotoxicity against BA.2 was stronger in seropositive individuals after one dose.

## Abstract

More than half of the BBIBP-CorV vaccines, outside of Pacific Asia, were distributed in Africa. Nevertheless, there are limited data on the immunogenicity of BBIBP-CorV from Africa. We compared the antibody response, after 1 and 2 doses of the BBIBP-CorV vaccine, in individuals seropositive or seronegative to severe acute respiratory syndrome coronavirus 2 prior to vaccination.

From March to May 2021, blood samples were obtained at first and second doses of the BBIBP-CorV, and 2 weeks later. Antibody titers against the full-length spike, receptor binding domain and nucleocapsid protein (anti-NC) of severe acute respiratory syndrome coronavirus 2 were measured. Pseudovirus neutralization assays and antibody-dependent cellular cytotoxicity (ADCC) against the D614G, BA.2, and BA.4 variants were also evaluated.

At the second dose, the immunoglobulin G titers for full-length spike and anti-nucleocapsid protein, the ADCC against BA-2, and the neutralizing activity against the D614G and BA.2 were higher in individuals seropositive to any of the epitopes at the first dose (n = 26) compared to the levels observed 2 weeks later in the seronegative group (n = 25). We did not observe an increase on magnitude of binding antibodies, ADCC, and neutralizing activities, in those seropositive, after the second homologous dose of the BBIBP-CorV vaccine.

We suggest that 1 dose of the BBIBP-CorV vaccine in seropositive individuals induced better antibodies response including against variant of concerns compared to that observed after 2 doses in seronegative individuals. A further homologous dose of the BBIBP-CorV vaccine, in those who are seropositive, does not improve the antibody response observed after the first dose.

One dose of the BBIBP-CorV vaccine in seropositive individuals induces better antibodies response compared to naïve individuals after 2 doses. A second dose within 3 weeks of the first dose does not further induced antibody response in seropositive individuals.