Alpha variant coronavirus outbreak in a nursing home despite high vaccination coverage: molecular, epidemiological and immunological studies.

Zürcher, Kathrin; Abela, Irene A; Stange, Madlen; Dupont, Carole; Mugglin, Catrina; Egli, Adrian; Trkola, Alexandra; Egger, Matthias; Fenner, Lukas (2023). Alpha variant coronavirus outbreak in a nursing home despite high vaccination coverage: molecular, epidemiological and immunological studies. Clinical infectious diseases, 77(4), pp. 537-546. Oxford 10.1093/cid/ciab1005

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Vaccination may control the COVID-19 pandemic, including in nursing homes where many high-risk people live. We conducted extensive outbreak investigations.


We studied an outbreak at a nursing home in Switzerland where vaccination uptake of mRNA vaccines against SARS-CoV-2 was 82% among residents as of Jan 21/2021. After a vaccinated symptomatic HCW was diagnosed with COVID-19 on Feb 22, we did an outbreak investigations in house A (47 residents, 37 HCWs) using SARS-CoV-2-specific PCR in nasopharyngeal swabs. We performed whole-genome sequencing of SARS-CoV-2 and serological analyses.


We identified 17 individuals with positive PCR tests; ten residents (five vaccinated) and seven HCWs (three vaccinated). Median age among residents was 86 years (interquartile range [IQR] 70-90) and 49 years (IQR 29-59) among HCWs. Among the five vaccinated residents, 60% had mild disease and had 40% no symptoms, whereas all five unvaccinated residents had mild to severe disease and two died. The vaccine effectiveness for the prevention of infection among the residents was 73.0% (95% Cl 24.7-90.1). The 12 available genomes were all alpha variants. Neutralizing titers were significantly higher in vaccinated individuals upon re-exposure (>1 week after diagnosis) than in vaccinated, unexposed HCWs (p=0.012). Transmission networks indicated four likely or possible transmissions from vaccinated to other individuals, and 12 transmission events from unvaccinated individuals.


COVID-19 outbreaks can occur in nursing homes, including transmission from vaccinated persons to others. Outbreaks might occur silently, underlining the need for continued testing and basic infection control measures in these high-risk settings.

Item Type:

Journal Article (Original Article)


04 Faculty of Medicine > Pre-clinic Human Medicine > Institute of Social and Preventive Medicine (ISPM)

UniBE Contributor:

Zürcher, Kathrin, Dupont, Carole, Mugglin, Catrina Andrea, Egger, Matthias, Fenner, Lukas


600 Technology > 610 Medicine & health
300 Social sciences, sociology & anthropology > 360 Social problems & social services






[4] Swiss National Science Foundation ; [211] NIH National Institute of Allergy and Infectious Diseases




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Date Deposited:

09 May 2022 09:15

Last Modified:

05 Oct 2023 08:18

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Uncontrolled Keywords:

B.1.1.7 COVID-19 UK variant nursing home outbreak vaccine




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