SARS-COV-2 Seroprevalence and Seroconversion Among Employees of the UZ Brussel Following COVID-19 Vaccination Using an Adenoviral Vector

December 11, 2025 updated by: Universitair Ziekenhuis Brussel

SARS-COV-2 Seroprevalence and Seroconversion Among Employees of the Universitair Ziekenhuis Brussel Following COVID-19 Vaccination Using an Adenoviral Vector

A novel zoonotic coronavirus was discovered in Wuhan (Hubei Province, China) mid-December 2019 and was named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The virus rapidly spread to the rest of the world, including Europe and explicitly affects the respiratory system, generating Coronavirus disease 2019 (COVID-19).

Employees of the university hospital of Brussels (UZ Brussel) presenting symptoms suggestive of COVID-19 are offered to be tested with real-time PCR on nasopharyngeal swabs. As asymptomatic infections have been described and as the PCR can be negative when taken late after onset of symptoms, serologic tests can be performed. The SARS-CoV 2003 epidemic demonstrated that serological assays were a useful diagnostic tool of non-acute infections. Although it is still uncertain whether convalescing patients have a risk of re-infection, recent data suggest that SARS-CoV-2 antibodies could protect at least for some time from subsequent viral exposures.

As the COVID-19 pandemic had devastating medical, economic and social consequences, safe and effective prophylactic vaccines were urgently needed. And thus several candidate vaccines against SARS-CoV-2 have been developed. The vaccination campaign of the health care workers of the UZ Brussel started mid January 2021. The first available vaccine was the BNT162b2 (Pfizer) vaccine. Early March 2021, in order to accelerate the vaccination of the UZ Brussel employees, the ChAdOx1 nCoV-19 (AZD12222) (Oxford, AstaZeneca) vaccination program was implemented in parallel with the BNT162b2 vaccination program In the COVEMUZ-2 study the investigators have already started to document the SARS-CoV-2 seroprevalence and seroconversion among vaccinated employees (using BNT162b2) in the UZ Brussels.

In this study, the investigators aim to prospectively document the SARS-CoV-2 seroprevalence and seroconversion among vaccinated employees (using ChAdOx1 nCoV-19) of the UZ Brussel, at three different time points, namely 6 weeks (+/- 2 weeks; T1), 6 months (+/- 1 month; T2) and 12 months (+/- 1 month; T3) after the second vaccination.

Study Overview

Status

Active, not recruiting

Conditions

Intervention / Treatment

Detailed Description

A novel zoonotic coronavirus was discovered in Wuhan (Hubei Province, China) mid-December 2019 and was named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The virus rapidly spread to the rest of the world, including Europe and explicitly affects the respiratory system, generating Coronavirus disease 2019 (COVID-19).

Employees of the university hospital of Brussels (UZ Brussel) presenting symptoms suggestive of COVID-19 are offered to be tested with real-time PCR on nasopharyngeal swabs. As asymptomatic infections have been described and as the PCR can be negative when taken late after onset of symptoms, serologic tests can be performed. The SARS-CoV 2003 epidemic demonstrated that serological assays were a useful diagnostic tool of non-acute infections. Although it is still uncertain whether convalescing patients have a risk of re-infection, recent data suggest that SARS-CoV-2 antibodies could protect at least for some time from subsequent viral exposures.

As the COVID-19 pandemic had devastating medical, economic and social consequences, safe and effective prophylactic vaccines were urgently needed. And thus several candidate vaccines against SARS-CoV-2 have been developed. The vaccination campaign of the health care workers of the UZ Brussel started mid January 2021. The first available vaccine was the BNT162b2 (Pfizer) vaccine. Early March 2021, in order to accelerate the vaccination of the UZ Brussel employees, the ChAdOx1 nCoV-19 (AZD12222) (Oxford, AstaZeneca) vaccination program was implemented in parallel with the BNT162b2 vaccination program In the COVEMUZ-2 study the investigators have already started to document the SARS-CoV-2 seroprevalence and seroconversion among vaccinated employees (using BNT162b2) in the UZ Brussels.

In this study, the investigators aim to prospectively document the SARS-CoV-2 seroprevalence and seroconversion among vaccinated employees (using ChAdOx1 nCoV-19) of the UZ Brussel, at three different time points, namely 6 weeks (+/- 2 weeks; T1), 6 months (+/- 1 month; T2) and 12 months (+/- 1 month; T3) after the second vaccination.

Study Type

Interventional

Enrollment (Estimated)

200

Phase

  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • Belgium
      • Brussels, Belgium, 1090
        • UZ Brussel

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

18 years and older (Adult, Older Adult)

Accepts Healthy Volunteers

Yes

Description

Inclusion Criteria:

  • Any adult employee of the UZ Brussel at T1 who has been vaccinated at the UZ Brussel with ChAdOx1 nCoV-19 vaccine between the 2nd of March and the 9th of March 2021 after participating to phase 4 of the COVEMUZ study between the 25th of January and the 12th of February and has provided a signed informed consent.

Exclusion Criteria:

  • UZ Brussel employees not active during the inclusion period (T1).

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Diagnostic
  • Allocation: N/A
  • Interventional Model: Single Group Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Other: General
All patients follow this arm. Patients will undergo 3 blood sample testings at 3 different time points and have to fill in a questionnaire at 3 different time points
Diagnostic test: Serological testing
Antibody testing for Sars-CoV-2 specific antibodies in blood + T cell immunity

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Seroprevalence
Time Frame: Change from baseline to 8 weeks, 6 months and 12 months timepoint
To document SARS-CoV-2 seroprevalence among employees of the UZ Brussel after ChAdOx1 nCoV-19 vaccination for SARS-CoV-2, at 8 (+/- 2) weeks after the first vaccination (T1); and 6 and 12 months after the first vaccination (T2 and T3) using a validated immuno-assay for detection of SARS-CoV-2 IgG antibodies
Change from baseline to 8 weeks, 6 months and 12 months timepoint
Seroconversion
Time Frame: Change from baseline to 8 weeks, 6 months and 12 months timepoint
To document SARS-CoV-2 seroconversion among employees of the UZ Brussel after ChAdOx1 nCoV-19 vaccination for SARS-CoV-2, at 8 (+/- 2) weeks after the first vaccination (T1); and 6 and 12 months after the first vaccination (T2 and T3) using a validated immuno-assay for detection of SARS-CoV-2 IgG antibodies
Change from baseline to 8 weeks, 6 months and 12 months timepoint

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
SARS-CoV-2 seroprevalence before and after vaccination
Time Frame: Change from baseline to 8 weeks, 6 months and 12 months timepoint
To compare the SARS-CoV-2 seroprevalence before vaccination with the SARS-CoV-2 prevalence after vaccination among employees of the UZ Brussel.
Change from baseline to 8 weeks, 6 months and 12 months timepoint
incidence of new definite cases
Time Frame: Change from baseline to 8 weeks, 6 months and 12 months timepoint
To document the incidence of new definite cases of COVID-19 (based on self-reported positive PCR testing on nasopharyngeal swab) among vaccinated employees of the UZ Brussel over a period of a year.
Change from baseline to 8 weeks, 6 months and 12 months timepoint
incidence of new probable cases
Time Frame: Change from baseline to 8 weeks, 6 months and 12 months timepoint
To document the incidence of new probable cases of COVID-19 (based on the study questionnaire filled in by the participants) among vaccinated employees of the UZ Brussel over a period of a year.
Change from baseline to 8 weeks, 6 months and 12 months timepoint
antibody kinetics of the SARS-CoV-2 specific antibodies using immunassays
Time Frame: Change from baseline to 8 weeks, 6 months and 12 months timepoint
To document the SARS-CoV-2 antibody kinetics after vaccination.
Change from baseline to 8 weeks, 6 months and 12 months timepoint
antigen-specificity of the SARS-CoV-2-specific T cells
Time Frame: Change from baseline to 8 weeks, 6 months and 12 months timepoint
To determine the antigen-specificity of the SARS-CoV-2-specific T cells as well as their phenotype and functionality
Change from baseline to 8 weeks, 6 months and 12 months timepoint
antibody neutralisation capacity of the SARS-CoV-2 specific B cells using immunassays
Time Frame: Change from baseline to 8 weeks, 6 months and 12 months timepoint
To document the SARS-CoV-2 antibody neutralisation capacity after vaccination.
Change from baseline to 8 weeks, 6 months and 12 months timepoint

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Universitair Ziekenhuis Brussel

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

May 5, 2021

Primary Completion (Estimated)

May 1, 2028

Study Completion (Estimated)

June 1, 2028

Study Registration Dates

First Submitted

April 22, 2021

First Submitted That Met QC Criteria

June 24, 2021

First Posted (Actual)

June 25, 2021

Study Record Updates

Last Update Posted (Estimated)

December 18, 2025

Last Update Submitted That Met QC Criteria

December 11, 2025

Last Verified

December 1, 2025

More Information

Terms related to this study

Additional Relevant MeSH Terms

Other Study ID Numbers

  • COVEMUZ-3

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

Clinical Trials on Covid19

Clinical Trials on Serological testing

Search Similar Trials

Sponsors and Collaborators

Medical Conditions

Drug Interventions

CROs by country

CROs in Macedonia

Conditions

Rare Diseases

Drug Interventions

Dietary Supplements

Sponsor/Collaborators

Locations

Subscribe