biostudies-literatureUnknown5(9)Buchan SA<h4>Importance</h4>The incidence of SARS-CoV-2 infection, including among individuals who have received 2 doses of COVID-19 vaccine, increased substantially following the emergence of the Omicron variant in Ontario, Canada. Understanding the estimated effectiveness of 2 or 3 doses of COVID-19 vaccine against outcomes associated with Omicron and Delta infections may aid decision-making at the individual and population levels.<h4>Objective</h4>To estimate vaccine effectiveness (VE) against symptomatic infections due to the Omicron and Delta variants and severe outcomes (hospitalization or death) associated with these infections.<h4>Design, setting, and participants</h4>This test-negative case-control study used linked provincial databases for SARS-CoV-2 laboratory testing, reportable diseaseJAMA network opene2232760https://www.ebi.ac.uk/biostudies/studies/S-EPMC9500552biostudies-literatureEstimated Effectiveness of COVID-19 Vaccines Against Omicron or Delta Symptomatic Infection and Severe Outcomes.PMC9500552Gubbay JBSundaram MEWilson KChung HFell DBSchwartz KLTadrous MNasreen SWilson SEBuchan SAKwong JCAustin PCBrown KAfalseEstimated Effectiveness of COVID-19 Vaccines Against Omicron or Delta Symptomatic Infection and Severe Outcomes.<h4>Importance</h4>The incidence of SARS-CoV-2 infection, including among individuals who have received 2 doses of COVID-19 vaccine, increased substantially following the emergence of the Omicron variant in Ontario, Canada. Understanding the estimated effectiveness of 2 or 3 doses of COVID-19 vaccine against outcomes associated with Omicron and Delta infections may aid decision-making at the individual and population levels.<h4>Objective</h4>To estimate vaccine effectiveness (VE) against symptomatic infections due to the Omicron and Delta variants and severe outcomes (hospitalization or death) associated with these infections.<h4>Design, setting, and participants</h4>This test-negative case-control study used linked provincial databases for SARS-CoV-2 laboratory testing, reportable disease2022-01-01T00:00:00Z2022 Sep2026-06-03T13:18:26.331Z2025-04-07T10:41:00.025ZS-EPMC95005523613633210.1001/jamanetworkopen.2022.32760