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- Title
Transmission Characteristics and Inactivated Vaccine Effectiveness Against Transmission of SARS-CoV-2 Omicron BA.5 Variants in Urumqi, China.
- Authors
Wang, Kai; Guo, Zihao; Zeng, Ting; Sun, Shengzhi; Lu, Yanmei; Wang, Jun; Li, Shulin; Luan, Zemin; Li, Huling; Zhang, Jing; Wang, Yida; Lu, Yaoqin; Zhao, Shi
- Abstract
This cohort study investigates transmission characteristics and vaccine effectiveness against transmission of SARS-CoV-2 Omicron BA.5 variants in China. Key Points: Question: What were the transmission characteristics of SARS-CoV-2 Omicron BA.5 variants, and was inactivated vaccine associated with a protective outcome against the transmission of these variants? Findings: This cohort study of 1139 individuals with COVID-19 found that despite active contact tracing, high vaccine coverage, and other intensive control measures, Omicron BA.5 variants had high risks of transmission in household settings and among younger and older individuals. Compared with a 2-dose inactivated vaccine, a booster dose was associated with a protective outcome against Omicron BA.5 transmission. Meaning: These findings suggest that there was high transmission risk of Omicron BA.5 variants but the combination of vaccine and nonpharmaceutical interventions may be associated with reduced transmission. Importance: In 2022, Omicron variants circulated globally, and Urumqi, China, experienced a COVID-19 outbreak seeded by Omicron BA.5 variants, resulting in the highest number of infections in the city's record before the exit of the zero COVID-19 strategy. Little was known about the characteristics of Omicron variants in mainland China. Objective: To evaluate transmission characteristics of Omicron BA.5 variants and the effectiveness of inactivated vaccine (mainly BBIBP-CorV) against their transmission. Design, Setting, and Participants: This cohort study was conducted using data from an Omicron-seeded COVID-19 outbreak in Urumqi from August 7 to September 7, 2022. Participants included all individuals with confirmed SARS-CoV-2 infections and their close contacts identified between August 7 and September 7, 2022 in Urumqi. Exposures: A booster dose was compared vs 2 doses (reference level) of inactivated vaccine and risk factors were evaluated. Main Outcomes and Measures: Demographic characteristics, timeline records from exposure to laboratory testing outcomes, contact tracing history, and contact setting were obtained. The mean and variance of the key time-to-event intervals of transmission were estimated for individuals with known information. Transmission risks and contact patterns were assessed under different disease-control measures and in different contact settings. The effectiveness of inactivated vaccine against the transmission of Omicron BA.5 was estimated using multivariate logistic regression models. Results: Among 1139 individuals diagnosed with COVID-19 (630 females [55.3%]; mean [SD] age, 37.4 [19.9] years) and 51 323 close contacts who tested negative for COVID-19 (26 299 females [51.2%]; mean [SD] age, 38.4 [16.0] years), the means of generation interval, viral shedding period, and incubation period were estimated at 2.8 days (95% credible interval [CrI], 2.4-3.5 days), 6.7 days (95% CrI, 6.4-7.1 days), and 5.7 days (95% CrI, 4.8-6.6 days), respectively. Despite contact tracing, intensive control measures, and high vaccine coverage (980 individuals with infections [86.0%] received ≥2 doses of vaccine), high transmission risks were found in household settings (secondary attack rate, 14.7%; 95% CrI, 13.0%-16.5%) and younger (aged 0-15 years; secondary attack rate, 2.5%; 95% CrI, 1.9%-3.1%) and older age (aged >65 years; secondary attack rate, 2.2%; 95% CrI, 1.5%-3.0%) groups. Vaccine effectiveness against BA.5 variant transmission for the booster-dose vs 2 doses was 28.9% (95% CrI, 7.7%-45.2%) and 48.5% (95% CrI, 23.9%-61.4%) for 15-90 days after booster dose. No protective outcome was detected beyond 90 days after the booster dose. Conclusions and Relevance: This cohort study revealed key transmission characteristics of SARS-CoV-2 as they evolved, as well as vaccine effectiveness against variants. These findings suggest the importance of continuously evaluating vaccine effectiveness against emerging SARS-CoV-2 variants.
- Subjects
CHINA; PREVENTION of infectious disease transmission; SARS-CoV-2; COVID-19; IMMUNIZATION; COVID-19 vaccines; GENETIC variation; RETROSPECTIVE studies; VACCINE effectiveness; INFECTIOUS disease transmission; INTERPERSONAL relations; RESEARCH funding; CONTACT tracing; STAY-at-home orders; LONGITUDINAL method; DISEASE risk factors
- Publication
JAMA Network Open, 2023, Vol 6, Issue 3, pe235755
- ISSN
2574-3805
- Publication type
Article
- DOI
10.1001/jamanetworkopen.2023.5755