Three doses of Sinovac's CoronaVac COVID-19 vaccine do not produce adequate levels of antibodies to fight the Omicron variant of the coronavirus, researchers from Hong Kong said in a statement.

Their analysis revealed Pfizer-BioNTech vaccine was more effective, as a third dose of the shot administered after two doses of the same or China's Sinovac vaccine provided 'protective levels' of antibody against Omicron.

Pfizer and its German partner BioNTech have said their three-shot course was able to neutralise the new Omicron variant in a laboratory test.

The latest study was conducted by researchers from the University of Hong Kong and the Chinese University of Hong Kong, and funded by the Health and Medical Research Fund and the Government of Hong Kong.

The statement did not say how many samples were used in the analysis. Sinovac did not immediately respond to a request for comment.

Sinovac's CoronaVac and state-owned Sinopharm's BBIBP-CorV vaccine are the two most-used vaccines in China and the leading COVID-19 vaccines exported by the country. Sinopharm also has a second vaccine in use in China.

Hong Kong has been using the Sinovac and Pfizer-BioNTech shots. But people aged 12-17 are eligible only for the BioNTech vaccine.