Abstract
IMPORTANCE Few studies have evaluated the waning of vaccine effectiveness against severe outcomes caused by SARS-CoV-2 Omicron infection. Hong Kong is providing inactivated and mRNA vaccines, but the population had limited protection from natural infections before the Omicron variant emerged.
OBJECTIVE To examine the change in vaccine effectiveness against hospitalization and mortality due to the Omicron variant over time.
DESIGN, SETTING, AND PARTICIPANTS This case-control study included adults with SARS-CoV-2 Omicron variant infection who died or were hospitalized in Hong Kong from January 1 to June 5, 2022 (ie, case participants), and adults with SARS-CoV-2 Omicron, sampled from the public health registry during the study period (ie, control participants), who were matched to case participants by propensity score. EXPOSURES Vaccination status of the individuals.
MAIN OUTCOMES AND MEASURES Estimated vaccine effectiveness against death, death or hospitalization, and death among hospitalized patients. Vaccine effectiveness was calculated as 1 − adjusted odds ratio obtained by conditional logistic regression adjusted with covariates for each period following vaccination.
RESULTS There were 32 823 case participants (25 546 [77.8%] 65 years; 16 930 [47.4%] female) and 131 328 control participants (100 041 [76.2%] 65 years; 66 625 [46.6%] female) in the sample analyzed for the death or hospitalization outcome. Vaccine effectiveness against death or hospitalization was maintained for at least 6 months after the second dose of both CoronaVac (74.0%; 95% CI, 71.8%-75.8%) and BNT162b2 (77.4%; 95% CI, 75.5%-79.0%) vaccines. Vaccine effectiveness against death in those aged 18 to 49 years was 86.4% (95% CI, 85.8%-87.0%) and 92.9% (95% CI, 92.6%-93.2%) for those receiving 2 doses of CoronaVac and BNT162b2, respectively, while for patients aged 80 years or older, it dropped to 61.4% (95% CI, 59.8%-63.2%) and 52.7% (95% CI, 50.2%-55.6%) for CoronaVac and BNT162b2, respectively. Nevertheless, overall vaccine effectiveness against death at 4 to 6 months after the third dose was greater than 90% for CoronaVac, BNT162b2, and the mixed vaccine schedule (eg, mixed vaccines: vaccine effectiveness, 92.2%; 95% CI, 89.2%-95.1%).
CONCLUSIONS AND RELEVANCE While vaccines were generally estimated to be effective against severe outcomes caused by SARS-CoV-2 Omicron infection, this analysis found that protection in older patients was more likely to wane 6 months after the second dose. Hence, a booster dose is (continued) Key Points Question Does vaccine effectiveness against hospitalization and mortality due to the SARS-CoV-2 Omicron variant change over time? Findings In this case-control study with 164 151 participants, the CoronaVac and BNT162b2 vaccines were generally estimated to be effective against severe outcomes due to SARS-CoV-2 Omicron infection, but protection among older individuals was more likely to wane 6 months after the second dose. Meaning These findings suggest that a booster dose should be recommended to older individuals to restore immunity, and this is especially urgent for a setting like Hong Kong, where third-dose coverage is still insufficient among older residents. + Supplemental content Author affiliations and article information are listed at the end of this article. Open Access. This is an open access article distributed under the terms of the CC-BY License. JAMA Network Open. 2023;6(2):e2254777. doi:10.1001/jamanetworkopen.2022.54777 (Reprinted) February 3, 2023 1/13 Confidential: Embargoed Until 11:00 am ET, February 03, 2023. Do Not Distribute Abstract (continued) recommended for older patients to restore immunity. This is especially critical in a setting like Hong Kong, where third-dose coverage is still insufficient among older residents
Estimation of Vaccine Effectiveness of CoronaVac and BNT162b2 Against Severe Outcomes Over Time Among Patients With SARS-CoV-2 Omicron
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JAMA Network Open EMBARGOED FOR RELEASE: 11 A.M. (ET), FRIDAY, FEBRUARY 3, 2023
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About The Study: In this case-control study with 164,000 participants, the CoronaVac and Pfizer-BioNTech vaccines were generally estimated to be effective against severe outcomes due to SARS-CoV-2 Omicron infection, but protection among older individuals was more likely to wane six months after the second dose. Hence, a booster dose is recommended for older patients to restore immunity.
Authors: Ka Chun Chong, Ph.D., and Eng Kiong Yeoh, M.B.B.S., of the Chinese University of Hong Kong, are the corresponding authors.
(doi:10.1001/jamanetworkopen.2022.54777)
Editor’s Note: Please see the article for additional information, including other authors, author contributions and affiliations, conflict of interest and financial disclosures, and funding and support.
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