The statement obtained by Nikkei Asia followed research from the University of Hong Kong that raised alarm this week in the dozens of countries that have received Sinovac’s CoronaVac shot.
The study, led by Professor Yuen Kwok-Yung, found that none of 25 Sinovac recipients produced sufficient levels of serum antibodies — a rough marker for protection against infection — to neutralise omicron.
“We believe this signifies that the vaccine effectiveness will drop against the omicron variant,” said Kelvin To, a clinical associate professor at Hong Kong University’s department of microbiology and a member of the study team.
As of Tuesday, the highly mutated strain of the coronavirus had reached 77 countries, according to the World Health Organization.
Omicron’s emergence has prompted some governments to clamp down on travel and other activity amid fears that it is more transmissible than earlier variants, even the highly infectious delta strain.
Pushing back against doubts over its vaccine, Sinovac said its own laboratory study showed seven out of 20 people who had received two CoronaVac jabs tested positive for neutralising antibodies, translating to a 35% efficacy rate.
Among 48 recipients of three doses, 45, or 94%, tested positive for the antibodies.
“These results suggest that a third dose of Sinovac’s vaccine was effective in improving the serum neutralisation against the omicron virus strain,” the company said.
Sinovac’s study was based on two omicron virus samples obtained from Hong Kong. The company said it is conducting further studies that involved serum samples with different antibody levels to comprehensively evaluate CoronaVac’s efficacy against omicron.
CoronaVac is one of two Chinese vaccines approved for emergency use by the WHO, out of a global list of eight.
The WHO said on Wednesday that preliminary evidence suggested existing Covid-19 vaccines might be less effective against omicron, but added that more data is needed to understand the risk of the variant evading immunity gained from either inoculation or previous infection.
Sinovac’s shot is not the only one drawing scrutiny. Another study by researchers at Hong Kong University and Hong Kong Chinese University found that the vaccine made by Pfizer’s German partner BioNTech may also be less effective against omicron.
An announcement on the study on Sunday revealed that BioNTech’s neutralisation was 32 times weaker against the variant than against the original strain of the virus that causes Covid-19.
Sinovac is the leading Chinese maker of Covid-19 vaccines by sales, having sold and supplied 808 million doses to 44 countries, according to figures updated Monday by Beijing-based Bridge Consulting, which tracks Chinese vaccines on a weekly basis.
The Asia-Pacific region accounted for 54% of the supplies, while Latin America, Europe and Africa took 28%, 13% and 5%, respectively.
To speed up distribution, the Beijing-headquartered company has signed packaging contracts with 10 countries, including Brazil and Indonesia.
For now, experts like those from Hong Kong University are urging the public to get booster shots when they become available, while vaccine makers work to develop a new generation of shots.
“There will be new variants coming up and most will likely escape the current vaccines, just like the influenza,” HKU’s To warned.