BACKGROUND AND AIMS
The COVID-19 pandemic is an ongoing global pandemic that is caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). The latest data available (as of 28th June 2021) indicate that >181 million cases have been confirmed. With >3.92 million confirmed deaths attributed to COVID-19, it is one of the deadliest pandemics in history.1 Prior to the pandemic, an established body of knowledge about the structure and function of pathogenic coronaviruses (causing SARS and Middle East respiratory syndrome) accelerated the development of various vaccine technologies during early 2020.2 As a result, a wide range of COVID-19 vaccines utilise strategies that generate antibody response to the receptor-binding domain of the spike protein of the virus.3 This ongoing widespread use of vaccines against SARS-CoV-2 has raised the important question on their ability to develop neutralising antibodies in levels sufficient to confer immunity to the COVID-19 infection. Moreover, the successful immunisation of healthcare professionals is of great importance and concern worldwide. The aim of this study was to evaluate the immunisation of healthcare professionals after a vaccination with the Pfizer/BioNTech BNT162b2 mRNA COVID-19 vaccine (Pfizer Inc., New York City, New York, USA; BioNTech SE, Mainz, Germany), using a quantitative measurement of IgG antibodies.
MATERIALS AND METHODS
A total of 198 health care professionals were included in the study. Blood samples were drawn approximately 2 weeks following the second dose of the vaccine, and the measurement of serum IgG antibodies against the spike domain of SARS-CoV-2 was performed using the SARS-CoV-2 IgG II Quant assay, a chemiluminescent microparticle immunoassay provided by Abbot Diagnostics (Abbot Laboratories, Abbot Park, Chicago, Illinois, USA).4-6 The SPSS 25.0 (IBM, Armonk, New York, USA) statistical package was used and p<0.05 was considered statistically significant.
Of the 198 (32.8%) health workers, 65 were male and 133 were female (67.2%) aged 47.8±10.3 years old. All participants developed sufficient IgG titres in the blood, with the majority of them (56.6%) being between 5,000–20,000 AU/mL (normal range: 50–25,000 AU/mL). Only three out of 198 (1.5%) had relatively low IgG levels (500–1,000 AU/mL) but none below the detection limit (<50 AU/mL). Of the 198 participants, 23 (11.6%) reported previous exposure to the virus approximately 2–3 months before vaccination. Half of them (12/23) had very high serum IgG levels (>25,000 AU/mL), while only 36 out of 175 persons with no history of previous illness had similar IgG levels (52.2% versus 20.6%; p=0.045) (Table 1).
The BNT162b2 mRNA COVID-19 vaccine offers high protection against SARS-CoV-2, as it was 100% effective in producing anti-SARS-CoV-2 spike antibodies. Most healthcare professionals with previous history of COVID-19 disease developed very high immune response; probably, the second dose of the vaccine is not necessary to be administered to people with previous history of COVID-19 disease.