BEIJING (BLOOMBERG) - Two doses and a booster of the Covid-19 vaccine made by China's Sinovac Biotech, one of the most widely used in the world, did not produce sufficient levels of neutralising antibodies to protect against the Omicron variant, a laboratory study has found.
For those who are fully immunised with the vaccine known as CoronaVac, getting a booster shot from Germany's BioNTech SE significantly improved protective levels of antibodies against Omicron, according to the study from the University of Hong Kong and The Chinese University of Hong Kong.
Two doses of the BioNTech shot, known as Comirnaty, were also insufficient, though adding a booster with the more potent mRNA vaccine raised protection to adequate levels, the researchers said in a statement.
The findings are in line with results disclosed by the vaccine-makers.
Last week, Sinovac released lab studies saying that 94 per cent of people getting three doses generated neutralising antibodies, though it did not say at what level.
The Hong Kong researchers set a threshold for what they considered a sufficient level of antibodies for protection based on earlier studies published in the journal Nature Medicine.
Sinovac officials did not immediately respond to calls seeking comment.
While much is still unknown about how Sinovac's shot holds up to Omicron - including how T cells, the immune system's weapon against virus-infected cells, will respond - the initial results are a blow to those who have received CoronaVac.
There have been more than 2.3 billion doses of the shot produced and shipped out, mostly in China and the developing world.
With Omicron seen to be about 70 times more transmissible than the Delta variant, the prospect of having to roll out a different booster shot or even re-vaccinate with a more Omicron-specific vaccine will set back the world's efforts to exit the pandemic.
The research, led by Dr Malik Peiris and Dr David Hui, examined the production of virus-neutralising antibodies in the blood of people vaccinated with the two shots currently in use in Hong Kong.
They confirm two doses of either vaccine was not sufficient to fend off Omicron.
The news comes as Hong Kong's medical advisers cleared the way for adults in the city to receive a booster shot, no matter which vaccine they initially received.
The new study suggests there are critical differences between them.