Superspreading of SARS-CoV-2 Omicron BA.2.23 among vaccinated Finnish adults: symptomatic COVID-19 only contracted by those without recent infection

Marianna Riekkinen; Mikael Kajova; Mari Eriksson; Annika Luukkainen; Ville Holmberg; Tuomas Aro; Sari H Pakkanen; Simo Miettinen; Reetta Montonen; Teemu Smura; Tinja Lääveri; Anu Kantele

doi:10.1017/S0950268823001024

Superspreading of SARS-CoV-2 Omicron BA.2.23 among vaccinated Finnish adults: symptomatic COVID-19 only contracted by those without recent infection

Epidemiol Infect. 2023 Jul 4:151:e113. doi: 10.1017/S0950268823001024.

Authors

Marianna Riekkinen^{1

2

3}, Mikael Kajova^{1

2

3}, Mari Eriksson¹, Annika Luukkainen¹, Ville Holmberg^{1

2}, Tuomas Aro^{1

2}, Sari H Pakkanen^{2

3}, Simo Miettinen^{4

5}, Reetta Montonen^{4

5}, Teemu Smura^{4

5}, Tinja Lääveri^{1

2

6}, Anu Kantele^{1

2

3}

Affiliations

¹ Department of Infectious Diseases, Inflammation Centre, Helsinki University Hospital and University of Helsinki, Helsinki, Finland.
² Human Microbiome Research Unit, University of Helsinki, Helsinki, Finland.
³ Meilahti Vaccine Research Centre, MeVac, University of Helsinki and Helsinki University Hospital, Helsinki, Finland.
⁴ Department of Virology, Faculty of Medicine, University of Helsinki, Helsinki, Finland.
⁵ HUS Diagnostic Centre, HUSLAB, Clinical Microbiology, University of Helsinki and Helsinki University Hospital, Helsinki, Finland.
⁶ Department of Computer Science, Aalto University, Espoo, Finland.

Abstract

An outbreak of SARS-CoV-2 was confirmed after an academic party in Helsinki, Finland, in 2022. All 70 guests were requested to fill in follow-up questionnaires; serologic analyses and whole-genome sequencing (WGS) were conducted when possible.Of those participating - all but one with ≥3 vaccine doses - 21/53 (40%) had test-confirmed symptomatic COVID-19: 7% of those with earlier episodes and 76% of those without. Half (11/21) were febrile, but none needed hospitalisation. WGS revealed subvariant BA.2.23.Compared to vaccination alone, our data suggest remarkable protection by hybrid immunity against symptomatic infection, particularly in instances of recent infections with homologous variants.

Keywords: COVID-19; Omicron; SARS-CoV-2; hybrid immunity; superspreading event.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

COVID-19* / prevention & control
Disease Outbreaks
Fever
Finland / epidemiology
Humans
SARS-CoV-2 / genetics