An Abu Dhabi-led study has shown that a protein-based COVID-19 vaccine made by Sinopharm, when given as a booster shot, after two doses of an earlier shot from the Chinese firm, gave a stronger antibody response against the omicron variant than a third dose of the original.

The authors of the study, which was published on Tuesday and had not been peer reviewed, included researchers from Sinopharm’s units and Sheikh Khalifa Medical City in Abu Dhabi. They cautioned that it remained unclear for how long Sinopharm’s NVSI-06-07 booster’s effect would last.

In December, the United Arab Emirates approved emergency use of Sinopharm’s protein-based COVID-19 vaccine, and it will be available to the public as a booster dose starting January 2022, the health ministry said at the time.

The Ministry of Health and Prevention approved the recombinant protein-based vaccine last month ahead of a planned roll-out this month.

The new study came amid concerns over the effectiveness of Sinopharm’s BBIBP-CorV shot, one of the two leading COVID-19 vaccines exported by China, against the omicron variant.

An earlier study showed a BBIBP-CorV booster had weaker neutralization against omicron than against an older coronavirus strain from the central Chinese city of Wuhan.

Sinopharm’s NVSI-06-07 protein-based vaccine adopts a different technology than the BBIBP-CorV shot that contains an inactivated form of the coronavirus.

The Sinopharm CNBG recombinant protein-based vaccine uses an S protein that surrounds the COVID-19 virus, which helps the body identify the virus and fight it in case of exposure.

The technology “will help in the prevention of several variants,” the UAE’s National Emergency Crisis and Disaster Management Authority (NCEMA) tweeted at the time.

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.

In the UAE, NCEMA said Sinopharm CNBG recombinant protein-based vaccine may be given to people over the age of 18 as a booster shot six months after receiving the Sinopharm vaccine.

Individuals allergic to any of the vaccine components are exempted after undergoing evaluations conducted by the medical team. Pregnant women, nursing mothers, and those planning pregnancy within the next six months are exempted from the vaccine but may receive other types of authorized vaccines.

Authorities are urging everyone to get a booster jab, with NCEMA saying: “Booster shots are among the key factors that help protect the health and safety of the community, as they play an effective role in boosting collective immunity.”