Analysis of SARS-CoV-2 antibodies and serum virus neutralisation in vaccinated heath care personnel. Analysis of virus neutralisation as a function of age, gender, and history of COVID-19 infection.
This study is an observational study with subsequent use of coded biological material. Sera
of Universitiy Hospital of Zurich (USZ) personnel vaccinated with BNT162b2 (BioNTech/Pfizer)
was analyzed for SARS-CoV-2 specific antibodies and virus neutralization.
Serum was analysed for virus-specific IgG and IgA using ELISA kits from Euroimmun (Kriens,
Switzerland) according to the manufacturer's instruction. IgG was determined with the
quantitative Anti-SARS-CoV-2 Quantivac kit and IgA was determined with the semi-quantitative
Anti-SARS-CoV-2 kit The kits determine antibodies against the spike-1 protein. The sera were
not diluted and not heat-inactivated prior to testing. The developed 96-well plates were
analysed by reading absorbance at 450 nm using an ELx808 ELISA reader from BioTek Instr. Inc.
In addition, a SARS-CoV-2 neutralization assay was developed at the department. In this
Tissue Culture Infection Dose (TCID) assay, Vero cells were infected with live SARS-CoV-2,
and sera were added at various dilutions to test the potential to neutralize viral infection.
The assay was conducted in a biosafety level 3 lab. Briefly, VERO-E6 cells were grown
overnight to ca. 80-90% adherence in flat-bottom 96-well cell culture plates. The SARS-CoV-2
was then mixed in round-bottom 96 well titre plates with 2-fold serial dilutions of serum and
incubated. The virus-serum mixture was then added to the VERO-E6 cell, and the cultures were
incubated again. After three days, the cultures were fixed by addition of paraformaldehyde
and stained with crystal violet for visualisation of cytotoxicity. The highest serum dilution
preventing infections of the cells was defined as the neutralization titre.
Procedure: Venous bleeding
Blood samples collected 5 times with approx. 2-4 weeks interval
Inclusion Criteria:
- Employed at the USZ Department of Dermatology
- Vaccinated against Covid-19 at USZ
- Male and female persons of any age
- Serum samples collected in 2020 or until June 11th 2021
- The subject was informed and gave his/her consent to the research project (non-coded
samples and data) and to publish data obtained from analysis of own biological samples
Exclusion Criteria:
- Known clinical relevant disease, e.g. immune suppressed by drugs or disease
- Documented objection of subsequent use and publication of biological samples and
personal health data
Univeristy Hospital Zurich
Zurich, Switzerland
Pål Johansen, Prof, Principal Investigator
University of Zurich, Dept. Dermatology