3 doses of Sinovac vaccine fail to protect against variant: Researchers

HONG KONG • 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 found.

For those who are fully vaccinated with the Sinovac vaccine, getting a booster shot from the vaccine made by American pharmaceutical giant Pfizer and German firm BioNTech 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 Pfizer-BioNTech shot were also insufficient, though adding a booster with the more potent mRNA vaccine raised protection to adequate levels, the researchers said. The findings are in line with results disclosed by the vaccine makers.

Last week, Sinovac released lab studies and said that 94 per cent of people getting three doses generated neutralising antibodies, though it did not say 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.

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 Sinovac's vaccine.

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 people with a more Omicron-specific vaccine will set back the world's efforts to end the pandemic.

The research, led by Professor Malik Peiris and Professor David Hui, examined the production of virus-neutralising antibodies in the blood of people vaccinated with the two shots currently in use in the city. They confirmed that two doses of either vaccine were not sufficient to fend off Omicron.

Hong Kong will administer Covid-19 booster shots to all adults from Jan 1, six months after their second dose.

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