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Effectiveness of COVID-19 Vaccination Against SARS-CoV-2 Omicron Variant in Two Outbreaks in Indoor Entertainment Settings in Australia

10 Pages Posted: 23 Feb 2022

See all articles by Bette Liu

Bette Liu

University of New South Wales (UNSW) - School of Public Health & Community Medicine

Sandrine Stepien

National Centre for Immunisation Research and Surveillance

Victoria Pye

Ministry of Public Health

Charlee Law

Hunter New England Local Health District

Craig Dalton

University of Newcastle

David Durrheim

University of Newcastle

Kristine Macartney

Children’s Hospital at Westmead - The National Centre for Immunisation Research and Surveillance (NCIRS)

More...

Abstract

Background: We estimate vaccine effectiveness against the SARS-CoV-2 B.1.1.529 (Omicron) variant in two outbreaks in indoor entertainment settings: a nightclub and a graduation ball at an exhibition centre in Australia shortly after the emergence of Omicron.

Methods: SARS-CoV-2 testing status of individuals registered as attending each event were obtained and matched to the Australian Immunisation Register. Individuals were classified as having 2 or 3 valid doses of a COVID-19 vaccine if dose receipt date was ≥14 days before the exposure date. Attack rates were compared between the unvaccinated and vaccinated, and rate ratios and vaccine effectiveness was estimated.

Findings: Following exposure at each venue, 295/535 (55.1%) and 102/189 (54.0%) individuals tested positive for SARS-CoV-2 (mean: 5 days post-event). The majority had at least 2 valid vaccine doses: nightclub: 95.0% (508/535); ball: 97.9% (185/189). In the nightclub, vaccine effectiveness (VE) of at least 2 doses given approximately 2 months earlier was -11.8% (95%CI -74.5 to 28.3%). At the ball, VE of at least 2 doses given approximately 3 months earlier was 46.5% (95%CI 38.8 to 53.2%) but the unvaccinated reference group was small (n=3); VE was higher with shorter interval since second dose receipt, VE 87.5% (95%CI 64.0 to 95.7%), 60.0% (95%CI 38.0 to 74.2%) and 32% (95%CI 22.0 to 40.6%) at 1-<2, 2-<3 and 3+ months respectively; no differences in VE were found between 2 or 3 doses (p=0.94). In both settings there was no evidence of different effectiveness by vaccine brand (primary course of Pfizer, AstraZeneca, Moderna COVID-19 vaccines).

Interpretation: The Omicron SARS-CoV-2 variant caused high attack rates in a two-dose vaccinated population in these high-risk indoor settings. Recent vaccination appears moderately effective against infection, but this varies depending on the setting, emphasising the importance of public health and social measures in addition to boosters to maximise protection.

Funding: NSW Health

Declaration of Interest: None to declare.

Ethical Approval: This report was conducted as part of NSW Health public health surveillance and outbreak management and as such no formal ethical approval was required.

Keywords: SARS-CoV-2, Omicron, Vaccine effectiveness, outbreak investigation

Suggested Citation

Liu, Bette and Stepien, Sandrine and Pye, Victoria and Law, Charlee and Dalton, Craig and Durrheim, David and Macartney, Kristine, Effectiveness of COVID-19 Vaccination Against SARS-CoV-2 Omicron Variant in Two Outbreaks in Indoor Entertainment Settings in Australia. Available at SSRN: https://ssrn.com/abstract=4026084 or http://dx.doi.org/10.2139/ssrn.4026084

Bette Liu (Contact Author)

University of New South Wales (UNSW) - School of Public Health & Community Medicine ( email )

Australia

Sandrine Stepien

National Centre for Immunisation Research and Surveillance ( email )

Australia

Victoria Pye

Ministry of Public Health ( email )

Kabul
Kabul
Afghanistan

Charlee Law

Hunter New England Local Health District ( email )

Wallsend
Australia

Craig Dalton

University of Newcastle ( email )

5 Barrack Road
Devonshire Building
NEWCASTLE UPON TYNE, NE1 7RU
United Kingdom

David Durrheim

University of Newcastle ( email )

5 Barrack Road
Devonshire Building
NEWCASTLE UPON TYNE, NE1 7RU
United Kingdom

Kristine Macartney

Children’s Hospital at Westmead - The National Centre for Immunisation Research and Surveillance (NCIRS) ( email )

Westmead
Australia

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