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. 2024 Jun 19;12(6):682.
doi: 10.3390/vaccines12060682.

Hybrid Immunity and the Incidence of SARS-CoV-2 Reinfections during the Omicron Era in Frontline Healthcare Workers

Carmen-Daniela Chivu  1   2 , Maria-Dorina Crăciun  1   2 , Daniela Pițigoi  1   3 , Victoria Aramă  3   4 , Monica Luminița Luminos  3   5 , Gheorghiță Jugulete  3   5 , Viorela Gabriela Nițescu  2   6 , Andreea Lescaie  2   6 , Cătălin Gabriel Apostolescu  3   4 , Adrian Streinu Cercel  3   4
Affiliations

Hybrid Immunity and the Incidence of SARS-CoV-2 Reinfections during the Omicron Era in Frontline Healthcare Workers

Carmen-Daniela Chivu et al. Vaccines (Basel). .

Abstract

During the coronavirus disease (COVID-19) pandemic healthcare workers (HCWs) acquired immunity by vaccination or exposure to multiple variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Our study is a comparative analysis between subgroups of HCWs constructed based on the number of SARS-CoV-2 infections, vaccination, and the dominant variant of SARS-CoV-2 in the population. We collected and analyzed data using the χ2 test and density incidence of reinfections in Microsoft Excel for Mac, Version 16.84, and MedCalc®, 22.026. Of the 829 HCWs, 70.1% (581) had only one SARS-CoV-2 infection and 29.9% (248) had two infections. Of the subjects with two infections, 77.4% (192) worked in high-risk departments and 93.2% (231) of the second infections were registered during Omicron dominance. The density incidence of reinfections was higher in HCWs vaccinated with the primary schedule than those vaccinated with the first booster, and the incidence ratio was 2.8 (95% CI: 1.2; 6.7). The probability of reinfection was five times lower (95% CI: 2.9; 9.2) in HCWs vaccinated with the primary schedule if the first infection was acquired during Omicron dominance. The subjects vaccinated with the first booster had a density incidence of reinfection three times lower (95% CI: 1.9; 5.8) if the first infection was during Omicron. The incidence ratio in subgroups constructed based on characteristics such as gender, age group, job category, and department also registered significant differences in density incidence. The history of SARS-CoV-2 infection by variant is important when interpreting and understanding public health data and the results of studies related to vaccine efficacy for hybrid immunity subgroup populations.

Keywords: SARS-CoV-2; healthcare workers; reinfection; vaccines protection; variant of concern.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
The workflow diagram of the HCWs study in the National Institute for Infectious Diseases “Professor Dr. Matei Balș”, Bucharest, Romania, January 2022–May 2023.
Figure 2
Figure 2
Graphical representation of cumulative data regarding vaccination status, first and second SARS-CoV-2 infections in HCWs included in the study.
See this image and copyright information in PMC

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