• Francisco Tsz Tsun Lai, Vincent Ka Chun Yan, Xuxiao Ye, Tiantian Ma, Xiwen Qin, Celine Sze Ling Chui, Xue Li, Eric Yuk Fai Wan, WongCarlos King HoCKHCentre for Safe Medication Practice and Research, Department of Pharmacology and Pharmacy (Lai, Yan, Ye, Ma, Qin, X. Li, Wan, C.K.H. Wong, C.L. Cheung, I.C.K. Wong, Chan), Li Ka Shing Faculty of Medicine, The University of Hong Kong; , Ching Lung Cheung, Philip Hei Li, Bernard Man Yung Cheung, Chak Sing Lau, WongIan Chi KeiICKCentre for Safe Medication Practice and Research, Department of Pharmacology and Pharmacy (Lai, Yan, Ye, Ma, Qin, X. Li, Wan, C.K.H. Wong, C.L. Cheung, I.C.K. Wong, Chan), Li Ka Shing Faculty of Medicine, The University of Hong Kong; Lab, and ChanEsther Wai YinEWYCentre for Safe Medication Practice and Research, Department of Pharmacology and Pharmacy (Lai, Yan, Ye, Ma, Qin, X. Li, Wan, C.K.H. Wong, C.L. Cheung, I.C.K. Wong, Chan), Li Ka Shing Faculty of Medicine, The University of Hong Kong; .
• Centre for Safe Medication Practice and Research, Department of Pharmacology and Pharmacy (Lai, Yan, Ye, Ma, Qin, X. Li, Wan, C.K.H. Wong, C.L. Cheung, I.C.K. Wong, Chan), Li Ka Shing Faculty of Medicine, The University of Hong Kong; Laboratory of Data Discovery for Health (Lai, Ma, Chui, X. Li, Wan, C.K.H. Wong, C.L. Cheung, I.C.K. Wong, Chan), Hong Kong Science and Technology Park; School of Nursing (Chui) and of Public Health (Chui) and Departments of Medicine (X. Li, P.H. Li, B.M.U. Cheung, Lau) and of Family Medicine and Primary Care, School of Clinical Medicine (Wan, C.K.H. Wong), Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China; Aston Pharmacy School (I.C.K. Wong), Aston University, Birmingham, UK.
• CMAJ. 2023 Jan 30; 195 (4): E143E152E143-E152.

BackgroundMultimorbidity is a prevalent risk factor for COVID-19-related complications and death. We sought to evaluate the association of homologous booster vaccination using BNT162b2 (Pfizer-BioNTech) or CoronaVac (Sinovac) with COVID-19-related deaths among people with multimorbidity during the initial Omicron wave of the COVID-19 pandemic.MethodsUsing routine clinical records from public health care facilities in Hong Kong, we conducted a territory-wide retrospective cohort study comparing people aged 18 years or older with 2 or more chronic conditions who received a homologous booster (third) dose with those who received only 2 doses, between Nov. 11, 2021, and Mar. 31, 2022. The primary outcome was death related to COVID-19.ResultsWe included 120 724 BNT162b2 recipients (including 87 289 who received a booster), followed for a median of 34 (interquartile range [IQR] 20-63) days and 127 318 CoronaVac recipients (including 94 977 who received a booster), followed for a median of 38 (IQR 22-77) days. Among BNT162b2 recipients, booster-vaccinated people had fewer COVID-19-related deaths than those who received 2 doses (5 v. 34, incidence rate 1.3 v. 23.4 per million person-days, weighted incidence rate ratio [IRR] 0.05, 95% confidence interval [CI] 0.02-0.16). We observed similar results among recipients of CoronaVac booster vaccination compared with those who received only 2 doses (26 v. 88, incidence rate 5.3 v. 53.1 per million person-days, weighted IRR 0.08, 95% CI 0.05-0.12).InterpretationAmong people with multimorbidity, booster vaccination with BNT162b2 or CoronaVac was associated with reductions of more than 90% in COVID-19-related mortality rates compared with only 2 doses. These results highlight the crucial role of booster vaccination for protecting vulnerable populations as the COVID-19 pandemic continues to evolve.© 2023 CMA Impact Inc. or its licensors.

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