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 the 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 antibodies against Omicron.

Pfizer and its German partner BioNTech have said...