2022
DOI: 10.1101/2021.12.30.21268565
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Effectiveness of COVID-19 vaccines against Omicron or Delta symptomatic infection and severe outcomes

Abstract: Background The incidence of SARS-CoV-2 infection, including among those who have received 2 doses of COVID-19 vaccines, has increased substantially since Omicron was first identified in the province of Ontario, Canada. Methods Applying the test-negative design to linked provincial data, we estimated vaccine effectiveness against infection (irrespective of symptoms or severity) caused by Omicron or Delta between November 22 and December 19, 2021. We included individuals who had received at least 2 COVID-19 va… Show more

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Cited by 134 publications
(145 citation statements)
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“…The third dose of the vaccine was associated with a similar reduction in the risk of hospitalisation for Omicron and Delta compared with their respective unvaccinated cases (86% and 88%, respectively). These findings concur with reports from UK [ 6 ] and are expected, based on data from studies that estimated reduced vaccine effectiveness against Omicron infection [ 9 - 12 ] and the benefit of a booster dose [ 9 , 10 ].…”
Section: Discussionsupporting
confidence: 91%
“…The third dose of the vaccine was associated with a similar reduction in the risk of hospitalisation for Omicron and Delta compared with their respective unvaccinated cases (86% and 88%, respectively). These findings concur with reports from UK [ 6 ] and are expected, based on data from studies that estimated reduced vaccine effectiveness against Omicron infection [ 9 - 12 ] and the benefit of a booster dose [ 9 , 10 ].…”
Section: Discussionsupporting
confidence: 91%
“…Although the efficacy of all vaccines appears to be reduced against the delta (B.1.617.2) and omicron (B.1.1.529) variants, BNT162b2, ChAdOx1, and others have shown high protection against COVID-19-related admissions to hospital and deaths. 15 …”
Section: Introductionmentioning
confidence: 99%
“…Pre-test probabilities of infection were assumed to be similar for unvaccinated and vaccinated individuals if vaccination constituted 1 or 2 doses, and the second dose was administered more than 2 months ago. 4 In light of the results of our meta-analysis (Figure 1) and the likely increase in sensitivity of rapid antigen tests to detect infectious Omicron cases when using a combined oral-nasal sample, we assume a sensitivity of 60% for rapid antigen tests when using a combined sample, and a specificity of 99.5%. [18][19][20] We therefore estimate a positive likelihood ratio of 0.60/(1-0.995) = 120, indicating that a positive test is highly predictive of an infectious case when using a combined oral-nasal sample.…”
Section: Figure 6 Estimated Probability Of Infectious Case After a Po...mentioning
confidence: 96%
“…In contrast to previous variants, unvaccinated people and vaccinated people have similar pre-test probabilities of disease. 4 Consequently, unvaccinated people and vaccinated people also have similar post-test probabilities of disease, if vaccinated individuals have only received 1 or 2 doses, and the second dose was administered more than 2 months ago.…”
Section: Ability Of Rapid Antigen Tests To Detect or Rule Out Infecti...mentioning
confidence: 99%
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