China's Sinovac Vaccine 'Inadequate' Against Omicron Variant, New Study Shows

China's indigenous COVID-19 vaccine manufactured by biopharmaceutical company Sinovac Biotech failed to produce adequate antibodies to fight off the omicron variant, new research from the University of Hong Kong showed.

Both Sinovac's CoronaVac and the COVID-19 vaccine manufactured by Pfizer-BioNTech were found to produce "inadequate" antibody responses to the omicron variant, scientists who conducted the study said in a statement released Tuesday.

The study observed two groups of 25 people fully vaccinated with CoronaVac and Pfizer's vaccine, respectively. To test the vaccines' efficiency against omicron, scientists used two strains of the new variant — one from Nigeria and another from South Africa, where omicron was first detected.

All of those who received the Sinovac vaccine lacked detectable levels of virus-fighting antibodies, the South China Morning Post reported, citing the research from professors Yuen Kwok-yung, Kelvin To and Honglin Chen.

Five out of the 25 participants who were fully vaccinated with the Pfizer vaccine, meanwhile, had detectable levels — a "significant" reduction of 20 to 24%, Yuen and his team said.

Additionally, the Pfizer vaccine's "titer of neutralizing antibodies against the omicron variant has decreased by 36-40-fold," the scientists said.

"The omicron variant virus was able to reduce the effectiveness of two doses of COVID-19 vaccine, particularly against CoronaVac. Therefore, COVID-19 vaccine recipients or even those recovered COVID-19 patients may be at a higher risk of breakthrough or reinfection," they added.

The findings, which only looked at one aspect of the immune response, indicated that booster shots may be needed for both vaccines to provide enhanced protection, but further study was still needed to confirm this.

The scientists also indicated that new vaccines should be developed in response to the new strain.

"The public is advised to get a third dose of the vaccine as soon as possible while waiting for the next generation of more matched vaccine," the scientists said.

Omicron, which has been detected in more than 60 countries since it was first reported, appeared to cause "very mild" symptoms, according to medical experts.

A majority of the variant's initial cases were young and vaccinated people, data showed.