# Assessment of immune responses to a Comirnaty® booster following CoronaVac® vaccination in healthcare workers

## TL;DR

This study examines how healthcare workers' immune responses change after receiving an mRNA booster following an initial inactivated virus vaccine, focusing on antibody and cytokine levels.

## Contribution

The study provides new insights into immune response dynamics after mixing vaccine types and identifies potential protective cytokine markers.

## Key findings

- Neutralising antibodies decreased significantly 90 days after initial vaccination but increased after the booster dose.
- Vaccinated individuals showed higher IL-22 levels compared to COVID-19 patients, suggesting a protective role.
- Cytokine profiles differed between vaccinated individuals and COVID-19 patients, with higher MCP-1, IL-18, and IFN-γ in infected patients.

## Abstract

The immunological response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and immunisation is variable.

To describe the humoral immune response by correlating IgA and IgG antibodies with NAbs titration following CoronaVac® immunisation and an mRNA (Comirnaty®) booster among healthcare workers (HCWs) and to compare the cytokine and interleukin profiles between HCWs vaccinated with CoronaVac and coronavirus disease 2019 (COVID-19) infected patients.

Samples from 133 HCWs collected at 20 (T1) and 90 (T2) days after CoronaVac immunisation and 15 (T3) days after a booster dose with the Comirnaty vaccine were analysed for IgA and IgG EIA and neutralisation assay. Cytokine levels from vaccinated individuals at T1 day and COVID-19 patients were compared.

Neutralising antibodies (NAbs) were observed in 81.7% of participants at T1, but only 49.2% maintained detectable NAbs after 90 days. The booster dose increased NAbs response in all participants. The cytokines with the highest levels post-vaccination were IL-6 and MCP-1. The MCP-1, IL-18, and IFN- γ levels were higher in COVID-19 patients than in vaccinated HCWs, while IL-22 levels increased in the vaccinated HCWs group.

The neutralisation titres in the T2 samples decreased, and antibody levels detected at T2 showed a more significant reduction than the neutralisation. The higher IL-22 expression in immunised individuals compared to those with COVID-19 suggests that IL-22 may be beneficial in protecting against severe disease.