In a study from The University of Hong Kong, scientists found one of the first real-world estimates of vaccine effectiveness against omicron infections, irrespective of symptoms or severity.
They did a survey of 5,310 blood donors and other volunteers and estimated that three doses of the Comirnaty or CoronaVac vaccines were, respectively, 48% or 30% effective in preventing omicron infection shortly after vaccination, further improving shortly after a fourth dose.
The researchers expected protection from infection also relates to protection from the transmission, and this is one of the first reports suggesting vaccine-induced protection from omicron virus transmission.
However, vaccine effectiveness waned rapidly thereafter over 100 days.
Moreover, the researchers estimated that more than 45% of the Hong Kong population was infected between 1 January and 31 July 2022.
The SARS-CoV-2 omicron variant has demonstrated enhanced transmissibility and escape of vaccine-derived immunity.
Between 1 January to 31 July 2022, Hong Kong experienced an unprecedented fifth wave of COVID-19 infections driven predominantly by the omicron BA.2 subvariant.
As local COVID transmission before 2022 was minimal, population immunity to SARS-CoV-2 in Hong Kong was almost entirely vaccine-derived at the start of the wave.
In the study, the team estimated three and four doses of Comirnaty were 48% and 69% effective in preventing omicron infection, respectively, seven days after vaccination, waning to 26% and 35% by 100 days after vaccination.
Three and four doses of CoronaVac were 30% and 56% effective after seven days respectively, declining to 6% and 11% by 100 days.
Meanwhile, the researchers identified that more than 45% of the local population in Hong Kong was infected by SARS-CoV-2 between 1 January and 31 July 2022 (i.e., an infection attack rate of 45%).
Accordingly, official case counts, incorporating both Reverse Transcriptase-PCR (RT-PCR) testing and Rapid Antigen Testing (RAT) results, identified less than 41% of all infections.
The results indicate that booster vaccination using either the mRNA or inactivated vaccine platforms is effective in preventing SARS-CoV-2 omicron BA.2 infection in the short term.
This adds to previous studies demonstrating robust vaccine effectiveness in preventing severe disease and death.
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The study was conducted by Joseph T. Wu et al and published in Nature Medicine.
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