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Effectiveness of BNT162b2 and CoronaVac COVID-19 Vaccination Against Asymptomatic and Symptomatic Infection of SARS-CoV-2 Omicron BA.2 in Hong Kong
28 Pages Posted: 25 Aug 2022
More...Abstract
Background: COVID-19 vaccines provide protection against symptomatic infection requiring medical attention and against severe outcomes; however, there is less evidence on the effectiveness of BNT162b2 and CoronaVac vaccines and their booster regimens against asymptomatic or mild Omicron infections in the community.
Methods: In this prospective cohort study in a population that was generally infection-naïve prior to a large Omicron BA.2 wave, individuals aged 5 or above conducted weekly rapid antigen testing (RAT) with a self-collected pooled nasal and throat swab, regardless of symptom and exposure status during the Omicron BA.2 wave. The effectiveness of one, two, and three doses of vaccination were 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.
Findings: Of 8636 individuals included in the analysis, 7233 (84%) had received at least two doses, 3993 (46%) received booster doses and 903 (10%) reported an infection. No statistically significant protection was observed for one or two doses of BNT162b2 and CoronaVac. Statistically significant protection against SARS-CoV-2 asymptomatic and symptomatic Omicron infection was demonstrated for those received BNT162b2 booster and CoronaVac booster, with a VE of 41% (95% CI: 23%-55%) and 32% (95% CI: 9·0%-50%) respectively. The VE of BNT162b2 and CoronaVac booster was further increased to 51% (95% CI: 31%-65%) and 42% (95% CI: 15%-60%) for symptomatic Omicron infections respectively. A similar pattern of VE (56%, 95% CI: 23%-75%) was also conferred by BNT162b2 booster to individuals that received CoronaVac primary series.
Interpretation: Two doses did not provide significant protection against COVID-19 infection. However the receipt of BNT162b2 booster and CoronaVac booster was associated with a significantly lower risk of Omicron BA.2 infection and symptomatic infection.
Funding Information: This project was supported by the Henry Fok Foundation, and a special commissioned fund (Ref No. COVID-19FHB) from the Health Bureau of the Hong Kong SAR Government.
Declaration of Interests: BJC reports honoraria from AstraZeneca, Fosun Pharma, GlaxoSmithKline, Moderna, Pfizer, Roche, and Sanofi Pasteur. All other authors declare no competing interests.
Ethics Approval Statement: The community surveillance programme was reviewed and commissioned by the government as an emergency public health initiative during the rapid up-swing of the fifth wave of the COVID-19 pandemic in Hong Kong, and was exempted from a full ethics review. Informed consent was obtained from all individuals, allowing collection, storage and use of information for surveillance and anonymised research purposes.
Keywords: SARS-CoV-2, COVID-19, vaccine effectiveness, asymptomatic infection, symptomatic infection
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