SARS-CoV-2 seroprevalence among healthcare workers in a highly vaccinated Japanese medical center from 2020–2023

ABSTRACT

Infection-induced SARS-CoV-2 seroprevalence has been studied worldwide. At Juntendo University Hospital (JUH) in Tokyo, Japan, we have consistently conducted serological studies using the blood residue of healthcare workers (HCWs) at annual health examinations since 2020. In this 2023 study (n = 3,594), N-specific seroprevalence (infection-induced) was examined while univariate and multivariate logistic regression analyses were performed to compute ORs of seroprevalence with respect to basic characteristics of participants. We found that the N-specific seroprevalence in 2023 was 54.1%—a jump from 17.7% in 2022, and 1.6% in 2021—with 37.9% as non-PCR-confirmed asymptomatic infection cases. Those younger than 50 (adjusted OR = 1.62; p < .001) and recipients with 4 doses or less of vaccine had a higher risk to be N-positive, ranging from 1.45 times higher for the participants with 4 doses (p < .001) to 4.31 times higher for the participants with 1 dose (p < .001), compared to those with 5 or more doses. Our findings indicate that robust vaccination programs may have helped alleviate symptoms but consequently caused asymptomatic spread in this hospital, especially among younger HCWs. Although having four doses or less was found to be associated with higher risk of infection, the optimal constitution and intervals for effective booster vaccines warrant further investigations.

KEYWORDS:

• SARS-CoV-2
• COVID-19
• seropositive
• mRNA vaccine
• healthcare worker
• Japan

Acknowledgments

The authors thank Kristin Thurlby (Johnson County Community College, Overland Park, KS, USA) for her editorial advice on preparation of this brief report.

Author contributions

Prof Naito had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Concept and design: All authors.

Acquisition, analysis, or interpretation of data: All authors.

Drafting of the manuscript: Yan, Naito.

Critical revision of the manuscript for important intellectual content: All authors.

Statistical analysis: Yan, Nojiri, Urasaki.

Administrative, technical, or material support: Ito, Yamamoto, Horiuchi, Fukuda, Tabe.

Supervision: Hori, Takahashi.

All authors have approved this version to be published and agreed to be accountable for all aspects of the work.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

All data used in the study are shown in the figures and tables. There are no more data to disclose.

Supplementary material

Supplemental data for this article can be accessed on the publisher’s website at https://doi.org/10.1080/21645515.2024.2337984.

Additional information

Funding

This research was supported by Japan Agency for Medical Research and Development (AMED) [JP20fk0108472 to TN]. The funder had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation of the manuscript; or decision to submit the manuscript for publication.