J Korean Med Sci.  2022 May;37(17):e133. 10.3346/jkms.2022.37.e133.

Nosocomial Outbreak by Delta Variant From a Fully Vaccinated Patient

• Jung J
• Lee J
• Park H
• Lim YJ
• Kim EO
• Park MS
• Kim SH

• KMID: 2529703
• DOI: http://doi.org/10.3346/jkms.2022.37.e133

Abstract

Background
The potential for a nosocomial outbreak of coronavirus disease 2019 (COVID-19) from a fully vaccinated individual is largely unknown.
Methods
In October 2021, during the time when the delta variant was dominant, a nosocomial outbreak of COVID-19 occurred in two wards in a tertiary care hospital in Seoul, Korea. We performed airflow investigations and whole-genome sequencing (WGS) of the virus.
Results
The index patient developed symptoms 1 day after admission, and was diagnosed with COVID-19 on day 4 post-admission. He was fully vaccinated (ChAdOx1 nCoV-19) 2 months before the diagnosis. Three inpatients and a caregiver in the same room, two inpatients in an adjacent room, two inpatients in rooms remote from the index room, and one nurse on the ward tested positive. Also, two resident doctors who stayed in an on-call room located on the same ward tested positive (although they had no close contact), as well as a caregiver who stayed on an adjacent ward, and a healthcare worker who had casual contact with this caregiver. Samples from five individuals were available for WGS, and all showed ≤ 1 single-nucleotide polymorphism difference. CCTV footage showed that the index case walked frequently in the corridors of two wards. An airflow study showed that the air from the corridor flowed into the resident on-call room, driven by an air circulator that was always turned on.
Conclusion
Transmission of severe acute respiratory syndrome coronavirus 2 from a fully vaccinated index occurred rapidly via the wards and on-call room. Care must be taken to not use equipment that can change the airflow.

Keyword

SARS-CoV-2; COVID-19; Vaccination; Airborne Transmission

Figure

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  Fig. 1 Floor plan of wards A and ward B. Individuals with coronavirus disease 2019 are indicated by case number.

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  Fig. 2 Epidemic curve.HCW = healthcare worker, WGS = whole-genome sequencing.

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  Fig. 3 Phylogenetic tree of severe acute respiratory syndrome coronavirus 2 sequences from Asan Medical Center. A phylogenetic tree was constructed using the maximum likelihood method (1000 replicates) in MEGA X Software. Bootstrap scores are shown at each node. Different branch colors represent different clades and subclades. The scale bar indicates the number of nucleotide substitution per site.

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