Study explores SARS-CoV-2 seroprevalence among vaccinated hospital workers

A recent study posted to the medRxiv* preprint server determined the humoral responses against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) in vaccinated hospital workers.

Background

The coronavirus disease 2019 (COVID-19) pandemic has been a global health crisis for two years causing more than 456 million infections and over six million deaths. Researchers have extensively studied the pandemic and its etiologic agent, SARS-CoV-2, to understand its pathogenic mechanism and develop therapeutics comprehensively. Several studies have been performed to determine the seroprevalence of SARS-CoV-2 among the general population. As such, researchers of the current study have been prospectively assessing seroprevalence among workers at the University Medical Center Hamburg-Eppendorf since the start of the pandemic.

Ever since the reports of thromboembolism emerged among the recipients of AstraZeneca’s AZD1222 (Vaxzevria) vaccine, it was discontinued for use in people below the age of 60 years from March 2021 in Germany. This change led to heterologous primary vaccination and the second dose was either the Pfizer BNT162b2 or the Moderna mRNA-1273 vaccines.

Following a massive outburst of COVID-19 infections in the fall of 2021, a booster vaccine dose was approved for priority administration in vulnerable populations from October 2021. The booster vaccination program was expanded in December 2021 to cover the general population.

The study

In the present study, researchers carried out a seroprevalence study and assessed COVID-19 infection- and vaccination-induced immunity among the institutional health care workers. Serum samples were collected from the institution’s employees, as mentioned earlier, between January 17–31, 2022. COVID-19 vaccination and infection status were determined with REDcap, an online tool capturing electronic data designed by the authors.

The presence of antibodies against the receptor-binding domain (RBD) of the spike (S) protein was assessed by using a quantitative assay (Elecsys anti-S1-RBD-SARS-CoV-2). Similarly, anti-nucleocapsid (anti-NC) antibodies were detected with Elecsys anti-NC-SARS-CoV-2 Ig assay.

Results

About 697 hospital employees participated in the current study constituting around 6% of the University Medical Center's workforce. The participants’ median age was 40 years, and females represented 78.5% of the cohort. Most participants were involved in patient care, while only 99 were not associated with patient care. All except five participants had been vaccinated against SARS-CoV-2 with at least one dose. Five participants received four vaccine doses, and more than 92% had been vaccinated thrice.

Anti-S1-RBD antibodies were detected among those who received at least one vaccine dose with a median titer of 13,891 arbitrary units (AU)/ml. Anti-NC antibodies were detected in 62 people indicating prior COVID-19 infection. There were no anti-NC antibodies among the five individuals who received four doses of the COVID-19 vaccine. A previous COVID-19 infection significantly increased anti-S1-RBD titers among the vaccinated individuals. Antibody titers were higher among the heterologous vaccination group than individuals who received three doses of mRNA vaccines. There was no difference in the immune responses of individuals who received one dose of Vaxzevria and two doses of mRNA vaccine (AZD1222 + mRNA + mRNA vaccine) and those with Vaxzevria in primary vaccination (AZD1222 + AZD1222 + mRNA) and mRNA vaccine in the booster course.  

Multiple linear regression analysis identified age, time since booster vaccination, vaccination regimen, presence of antibodies against SARS-CoV-2 NC as significant predictors of anti-S1-RBD titers. Notably, the presence of anti-NC antibodies and time since booster were the only statistically significant factors. Analyzing the anti-S1-RBD titers in SARS-CoV-2-naïve individuals with their previous levels (from May 2021) revealed a massive increase in the antibody titers. A similar increase in the humoral response was observed among 222 out of the 251 individuals who had been doubly vaccinated during their previous visit (for serum collection), and by the current visit (January 2022) were boosted with a third dose. Only 26 workers had reduced antibody titers after the booster vaccination compared to their previous levels.

Conclusions

The researchers observed that the infection rate, indicated by the prevalence of anti-NC antibody titers, in January 2022 had doubled since their previous assessment during May 2021. The COVID-19 incidence rate was considerably lower among the hospital workers than the general population. In line with various studies, the authors reported that three exposures to the SARS-CoV-2 antigen through vaccine-induced or hybrid immunity (infection and two vaccinations) are required to generate robust humoral responses with high levels of antibodies. Their findings indicated the current infection control interventions were robust and effective in preventing nosocomial transmission.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Tarun Sai Lomte

Tarun is a writer based in Hyderabad, India. He has a Master’s degree in Biotechnology from the University of Hyderabad and is enthusiastic about scientific research. He enjoys reading research papers and literature reviews and is passionate about writing.