A medical worker prepares a dose of the Sinopharm COVID-19 coronavirus vaccine at a hospital in Wuhan in China's central Hubei province on Nov 25, 2021. (STR / AFP)

BEIJING – A protein-based COVID-19 vaccine made by Sinopharm, when given as a booster after two doses of an earlier shot from the Chinese firm, elicited a stronger antibody response against the Omicron variant than a third dose of the original, a study showed.

The study was published on Tuesday and had not been peer-reviewed.

READ MORE: Sinopharm leads delivery of COVID vaccines via COVAX

An earlier study showed a BBIBP-CorV booster made by Sinopharm had weaker neutralization against Omicron than against an older coronavirus strain. 

Sinopharm's NVSI-06-07 protein-based vaccine, approved for emergency use as a booster in the United Arab Emirates in December, adopts a different technology than the BBIBP-CorV shot that contains an inactivated form of the coronavirus

Sinopharm's NVSI-06-07 protein-based vaccine, approved for emergency use as a booster in the United Arab Emirates in December, adopts a different technology than the BBIBP-CorV shot that contains an inactivated form of the coronavirus.

Among 192 healthy adults vaccinated with two BBIBP-CorV doses for six months or longer, the neutralizing antibody level against Omicron in those later given a NVSI-06-07 booster was "significantly higher" than that in those who received a BBIBP-CorV third dose, researchers said in a paper.

The antibody-based results are different from the efficacy readings about how well the NVSI-06-07 booster after BBIBP-CorV vaccination would protect people from Omicron-caused disease.

ALSO READ: Sinopharm crosses 'critical threshold' on vaccines

The authors of the paper, including researchers from Sinopharm's units and Sheikh Khalifa Medical City in Abu Dhabi, cautioned that it remained unclear for how long the NVSI-06-07 booster's effect would last.