Effectiveness of BNT162b2 and Sinovac vaccines against the transmission of SARS-CoV-2 during Omicron-predominance in Hong Kong: A retrospective cohort study of COVID-19 cases.

In 2022, SARS-CoV-2 Omicron variants circulated globally, generating concerns about increased transmissibility and immune escape. Hong Kong, having an infection-naive population with a moderate 2-dose vaccine coverage (63% by the end of 2021), experienced a COVID-19 epidemic largely seeded by Omicron BA.2 variants that led to the greatest outbreak in the region to date. Little remains known about the protection of commonly-administered vaccines against transmission of Omicron BA.2 variants. In this retrospective cohort study, we identified 17 535 laboratory-confirmed COVID-19 cases using contact tracing information during the Omicron-predominant period between January and June 2022 in Hong Kong. Demographic characteristics, time from positive test result to case reporting, isolation, or hospital admission, as well as contact tracing history and contact setting were extracted. Transmission pairs were reconstructed through suspected epidemiological links according to contact tracing history, and the number of secondary cases was determined for each index case as a measurement for risk of transmission. The effectiveness of mRNA vaccine (BNT162b2) and inactivated vaccine (Sinovac) against transmission of BA.2 variants was estimated using zero-inflated negative binomial regression models. Vaccine effectiveness against transmission for patients who received the 2-dose BNT162b2 vaccine was estimated at 56.2% (95% CI: 14.5, 77.6), 30.6% (95% CI: 13.0, 44.6), and 21.3% (95% CI: 2.9, 36.2) on 15 - 90, 91 - 180, and 181 - 270 days after vaccination, respectively, showing a significant decrease over time. For 3-dose vaccines, vaccine effectiveness estimates were 41.0% (95% CI: 11.3, 60.7) and 41.9% (95% CI: 6.1, 64.0) on 15 - 180 days after booster doses of Sinovac and BNT162b2, respectively. Although significant vaccine effectiveness was detected in household settings, no evidence of such protective association was detected in non-household settings for either Sinovac or BNT162b2. Moderate and significant protection against Omicron BA.2 variants' transmission was found for 2 and 3 doses of Sinovac or BNT162b2 vaccines. Although protection by 2-dose BNT162b2 may evidently wane with time, protection could be restored by the booster dose. Here, we highlight the importance of continuously evaluating vaccine effectiveness against transmission for emerging SARS-CoV-2 variants.

Zhao S ，Guo Z ，Sun S ，Hung CT ，Leung EYM ，Wei Y ，Wang H ，Li K ，Yam CHK ，Chow TY ，Gao J ，Jia KM ，Chong KC ，Yeoh EK ... -  《-》

Effectiveness of BNT162b2 and CoronaVac COVID-19 vaccination against asymptomatic and symptomatic infection of SARS-CoV-2 omicron BA.2 in Hong Kong: a prospective cohort study.

COVID-19 vaccines provide protection against symptomatic infection that might require medical attention and against severe outcomes; however, there is a paucity of evidence regarding the effectiveness of the BNT162b2 and CoronaVac vaccines and their booster regimens against asymptomatic or mild omicron infections in the community. We aimed to measure the effectiveness of BNT162b2 and CoronaVac vaccines against asymptomatic and symptomatic SARS-CoV-2 omicron infections, during a period of omicron BA.2 predominance in Hong Kong. In this prospective cohort study in a population that was generally infection-naive before the large omicron BA.2 wave between January and late May, 2022, we established a public health surveillance platform to monitor the evolving activity of SARS-CoV-2 infections in the community. We recruited a cohort of individuals aged 5 years and older between March 1 and March 7, 2022, from the general population. Individuals were enrolled from all 18 districts of Hong Kong, according to a predefined age-stratified quota, primarily by random digit dialing (generating suitable eight-digit local telephone numbers by randomly picking sets of the first four digits from a sampling frame, and randomly generating the last four digits), and supplemented by our existing cohorts (which included cohorts for studying influenza vaccination from school-based vaccination programmes and cohorts for SARS-CoV-2 seroprevalence from the community), to ensure representativeness of the population in Hong Kong. Participants did weekly rapid antigen testing with a self-collected pooled nasal and throat swab, regardless of symptom and exposure status, from March 1 to April 15, 2022. Individuals reporting a history of SARS-CoV-2 infection confirmed by laboratory PCR testing before enrolment were excluded from the vaccine effectiveness analysis to avoid potential bias due to infection-induced immunity. The primary outcomes of the study were the incidence of SARS-CoV-2 infection, including asymptomatic and symptomatic infections, and the vaccine effectiveness of BNT162b2 and CoronaVac vaccines. The effectiveness of one, two, and three doses of vaccination was estimated with a Cox proportional hazards regression model with time-dependent covariates, allowing for changes in vaccination status over time, after adjustment for demographic factors and pre-existing medical conditions. Of the 8636 individuals included in the analysis, 7233 (84%) received at least two doses of vaccine, 3993 (46%) received booster doses, and 903 (10%) reported SARS-CoV-2 infection. Among these infections 589 (65·2%) were symptomatic and 314 (34·8%) were asymptomatic at the time of testing. Statistically significant protection against asymptomatic and symptomatic SARS-CoV-2 omicron infection was found only for those who received a BNT162b2 or CoronaVac booster dose, with a vaccine effectiveness of 41·4% (23·2 to 55·2; p=0·0001) and 32·4% (9·0 to 49·8; p=0·0098), respectively. The vaccine effectiveness of BNT162b2 and CoronaVac boosters was further increased to 50·9% (95% CI 31·0-65·0; p<0·0001) and 41·6% (15·0-59·8; p=0·0049), respectively, for symptomatic omicron infections. A similar pattern of vaccine effectiveness (55·8%, 22·9-74·6; p=0·0040) was also conferred after receipt of a BNT162b2 booster by individuals who received a CoronaVac primary vaccination series. Two doses of either vaccine did not provide significant protection against COVID-19 infection. However, receipt of a BNT162b2 booster or CoronaVac booster was associated with a significantly lower risk of omicron BA.2 infection and symptomatic infection. Our findings confirm the effectiveness of booster doses to protect against mild and asymptomatic infection. Henry Fok Foundation and Hong Kong Health Bureau.

Tsang NNY ，So HC ，Cowling BJ ，Leung GM ，Ip DKM ... -  《-》

Vaccine effectiveness of BNT162b2 and CoronaVac against SARS-CoV-2 omicron infection and related hospital admission among people with substance use disorder in Hong Kong: a matched case-control study.

People with substance use disorder have a high risk of SARS-CoV-2 infection and subsequent poor outcomes. Few studies have evaluated COVID-19 vaccine effectiveness among people with substance use disorder. We aimed to estimate the vaccine effectiveness of BNT162b2 (Fosun-BioNTech) and CoronaVac (Sinovac) against SARS-CoV-2 omicron (B.1.1.529) infection and related hospital admission in this population. We did a matched case-control study using electronic health databases in Hong Kong. Individuals diagnosed with substance use disorder between Jan 1, 2016, and Jan 1, 2022, were identified. People aged 18 years and older with SARS-CoV-2 infection from Jan 1 to May 31, 2022, and people with COVID-19-related hospital admission from Feb 16 to May 31, 2022, were included as cases and were matched by age, sex, and previous clinical history with controls from all individuals diagnosed with substance use disorder who attended the Hospital Authority health services: up to three controls for SARS-CoV-2 infection and up to ten controls for hospital admission. Conditional logistical regression was used to evaluate the association between vaccination status (ie, one, two, or three doses of BNT162b2 or CoronaVac) and the risk of SARS-CoV-2 infection and COVID-19-related hospital admission, adjusted for baseline comorbidities and medication use. Among 57 674 individuals with substance use disorder, 9523 people with SARS-CoV-2 infections (mean age 61·00 years, SD 14·90; 8075 [84·8%] males and 1448 [15·2%] females) were identified and matched to 28 217 controls (mean age 60·99 years, 14·67; 24 006 [85·1%] males and 4211 [14·9%] females), and 843 people with COVID-19-related hospital admissions (mean age 70·48 years, SD 14·68; 754 [89·4%] males and 89 [10·6%] females) were identified and matched to 7459 controls (mean age 70·24 years, 13·87; 6837 [91·7%] males and 622 [8·3%] females). Data on ethnicity were not available. We observed significant vaccine effectiveness against SARS-CoV-2 infection for two-dose BNT162b2 vaccination (20·7%, 95% CI 14·0-27·0, p<0·0001) and three-dose vaccination (all BNT162b2 41·5%, 34·4-47·8, p<0·0001; all CoronaVac 13·6%, 5·4-21·0, p=0·0015; BNT162b2 booster after two-dose CoronaVac 31·3%, 19·8-41·1, p<0·0001), but not for one dose of either vaccine or two doses of CoronaVac. Significant vaccine effectiveness against COVID-19-related hospital admission was detected after one dose of BNT162b2 vaccination (35·7%, 3·8-57·1, p=0·032), two-dose vaccination (both BNT162b2 73·3%, 64·3 to 80·0, p<0·0001; both CoronaVac 59·9%, 50·2-67·7, p<0·0001), and three-dose vaccination (all BNT162b2 86·3%, 75·6-92·3, p<0·0001; all CoronaVac 73·5% 61·0-81·9, p<0·0001; BNT162b2 booster after two-dose CoronaVac 83·7%, 64·6-92·5, p<0·0001), but not after one dose of CoronaVac. For both BNT162b2 and CoronaVac, two-dose or three-dose vaccination was protective against COVID-19-related hospital admission and the booster dose provided protection against SARS-CoV-2 infection among people with substance use disorder. Our findings confirm the importance of booster doses in this population during the period dominated by the omicron variant. Health Bureau, the Government of the Hong Kong Special Administrative Region.

Huang C ，Wei Y ，Yan VKC ，Ye X ，Kang W ，Yiu HHE ，Shami JJP ，Cowling BJ ，Tse ML ，Castle DJ ，Chui CSL ，Lai FTT ，Li X ，Wan EYF ，Wong CKH ，Hayes JF ，Chang WC ，Chung AKK ，Lau CS ，Wong ICK ，Chan EW ... -  《Lancet Psychiatry》

Transmission Characteristics and Inactivated Vaccine Effectiveness Against Transmission of SARS-CoV-2 Omicron BA.5 Variants in Urumqi, China.

Wang K ，Guo Z ，Zeng T ，Sun S ，Lu Y ，Wang J ，Li S ，Luan Z ，Li H ，Zhang J ，Wang Y ，Lu Y ，Zhao S ... -  《JAMA Network Open》

Omicron BA.1-specific T-cell responses in adults vaccinated with CoronaVac or BNT162b2 in Hong Kong: an observational cohort study.

The primary aim of using vaccines in public health responses to SARS-CoV-2 variants of concern is to reduce incidence of severe disease, for which T-cell responses are essential. There is a paucity of data on vaccine-induced T-cell immunity to omicron (B.1.1.529). We aimed to compare SARS-CoV-2 omicron BA.1-specific T-cell responses in adults vaccinated with CoronaVac or BNT162b2. For this observational cohort, we recruited adults (aged ≥18 years) from three vaccination centres in Hong Kong. We included participants from four cohorts (cohort 1: participants who received two doses of either BNT162b2 or CoronaVac, cohort 2: participants who received two doses and a booster, cohort 3: participants who received two doses and a booster and had a breakthrough omicron infection, and cohort 4: participants who had a previous non-omicron infection and subsequently received one dose of vaccine). People with confirmed history of COVID-19 at recruitment were excluded from cohort 1 and cohort 2. We collected blood samples before vaccination (for cohort 1 and 2), 1-month following vaccination (for all cohorts), and during convalescence for cohort 3 and 4) and determined the proportion of IFNγ+CD4+ and IFNγ+CD8+ T cells in peripheral blood against SARS-CoV-2 using flow cytometry with peptide pools of SARS-CoV-2 wild type or omicron BA.1. The primary outcome was proportion of CD4+ and CD8+ T cells against SARS-CoV-2 1 month after exposure (ie, vaccination or breakthrough infection). Overall, between May 21, 2020, and Aug 31, 2021, we recruited 659 participants (231 [35%] men and 428 [65%] women). Of these participants, 428 were included in cohort 1 (214 [50%] received BNT162b2 and 214 [50%] received CoronaVac); 127 in cohort 2 (48 [38%] received all BNT162b2, 40 [31%] received all CoronaVac, and 39 [31%] received two CoronaVac and a booster with BNT162b2); 58 in cohort 3, and 46 in cohort 4 (16 [35%] received CoronaVac and 30 [65%] received BNT162b2). Vaccine-induced T-cell responses to the wild-type and omicron BA.1 variants were generally similar in adults receiving two doses of either CoronaVac (CD4+ cells p=0·33; CD8+ cells p=0·70) or BNT162b2 (CD4+ cells p=0·28; CD8+ cells p=1·0). Using a peptide pool of all structural proteins for stimulation, BNT162b2 induced a higher median frequency of omicron-specific CD4+ T cells in adults younger than 60 years (CD4+ cells 0·012% vs 0·010%, p=0·031; CD8+ cells 0·003% vs 0·000%, p=0·055) and omicron-specific CD8+ T cells in people aged 60 years or older (CD4+ cells 0·015% vs 0·006%, p=0·0070; CD8+ cells 0·007% vs 0·000%, p=0·035). A booster dose of either BNT162b2 or CoronaVac after two doses of CoronaVac boosted waning T-cell responses, but T-cell responses did not exceed those at 1 month after the second dose (CoronaVac CD4+ p=0·41, CD8+ p=0·79; BNT162b2 CD4+ p=0·70 CD8+ p=0·80). The evidence that mRNA and inactivated vaccines based on the ancestral SARS-CoV-2 virus elicited T-cell responses to SARS-CoV-2 omicron variants might explain the high observed vaccine effectiveness against severe COVID-19 shown by both types of vaccine, despite great differences in neutralising antibody responses. The use of either vaccine can be considered if the primary aim is to reduce severity and death caused by the new omicron subvariants; however, BNT162b2 is preferable for adults older than 60 years. The Health and Medical Research Fund Commissioned Research on the Novel Coronavirus Disease and S H Ho Foundation.

Mok CKP ，Chen C ，Zhao S ，Sun Y ，Yiu K ，Chan TO ，Lai HL ，Lai KC ，Lau KM ，Ling KC ，Chan KKP ，Ng SS ，Ko FW ，Peiris M ，Hui DS ... -  《Lancet Microbe》