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BMC Medicine
Published in: BMC Medicine 1/2022

Open Access 01-12-2022 | Vaccination | Research article

Impact of a delayed second dose of mRNA vaccine (BNT162b2) and inactivated SARS-CoV-2 vaccine (CoronaVac) on risks of all-cause mortality, emergency department visit, and unscheduled hospitalization

Authors: Carlos King Ho Wong, Xi Xiong, Kristy Tsz Kwan Lau, Celine Sze Ling Chui, Francisco Tsz Tsun Lai, Xue Li, Esther Wai Yin Chan, Eric Yuk Fai Wan, Ivan Chi Ho Au, Benjamin John Cowling, Cheuk Kwong Lee, Ian Chi Kei Wong

Published in: BMC Medicine | Issue 1/2022

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Abstract

Background

Safety after the second dose of the SARS-CoV-2 vaccine remains to be elucidated, especially among individuals reporting adverse events after their first dose. This study aims to evaluate the impact of a delayed second dose on all-cause mortality and emergency services.

Methods

A territory-wide, retrospective cohort of people who had completed two doses of mRNA (BNT162b2) or inactivated SARS-CoV-2 (CoronaVac) vaccine between February 23 and July 3, 2021, in Hong Kong was analyzed, with linkage to electronic health records retrieved from the Hong Kong Hospital Authority. Vaccine recipients were classified as receiving a second dose within recommended intervals (21–28 days for BNT162b2; 14–28 days for CoronaVac) or delayed. Study outcomes were all-cause mortality, emergency department (ED) visits, and unscheduled hospitalizations within 28 days after the second dose of vaccination.

Results

Among 417,497 BNT162b2 and 354,283 CoronaVac second dose recipients, 3.8% and 28.5% received the second dose beyond the recommended intervals (mean 34.4 and 31.8 days), respectively. During the study period, there were < 5 daily new cases of COVID-19 infections in the community. Delaying the second dose was not associated with all-cause mortality (hazard ratio [HR] = 1.185, 95% CI 0.478–2.937, P = 0.714), risk of ED visit (HR = 0.966, 95% CI 0.926–1.008, P = 0.113), and risk of unscheduled hospitalization (HR = 0.956, 95% CI 0.878–1.040, P = 0.294) compared to that within the recommended interval for CoronaVac recipients. No statistically significant differences in all-cause mortality (HR = 4.438, 95% CI 0.951–20.701, P = 0.058), ED visit (HR = 1.037, 95% CI 0.951–1.130, P = 0.411), and unscheduled hospitalization (HR = 1.054, 95% CI 0.867–1.281, P = 0.597) were identified between people who received a second dose of BNT162b2 within and beyond the recommended intervals.

Conclusions

No significant association between delayed second dose of BNT162b2 or CoronaVac and all-cause mortality, ED visit, and unscheduled hospitalization was observed in the present cohort. Regardless of the recommended or delayed schedule for SARS-CoV-2 vaccination, a second dose of both vaccines should be administered to obtain better protection against infection and serious disease. The second dose should be administered within the recommended interval following the manufacturer’s product information, until further studies support the benefits of delaying vaccination outweighing the risks.
Appendix
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Metadata
Title
Impact of a delayed second dose of mRNA vaccine (BNT162b2) and inactivated SARS-CoV-2 vaccine (CoronaVac) on risks of all-cause mortality, emergency department visit, and unscheduled hospitalization
Authors
Carlos King Ho Wong
Xi Xiong
Kristy Tsz Kwan Lau
Celine Sze Ling Chui
Francisco Tsz Tsun Lai
Xue Li
Esther Wai Yin Chan
Eric Yuk Fai Wan
Ivan Chi Ho Au
Benjamin John Cowling
Cheuk Kwong Lee
Ian Chi Kei Wong
Publication date
01-12-2022
Publisher
BioMed Central
Published in
BMC Medicine / Issue 1/2022
Electronic ISSN: 1741-7015
DOI
https://doi.org/10.1186/s12916-022-02321-4

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