Beijing — A recent study showed that three doses of one of the world’s most widely used Covid-19 vaccines, China’s Sinovac, failed to produce sufficient levels of neutralising antibodies to protect against the Omicron variant.
The University of Hong Kong and The Chinese University of Hong Kong conducted a laboratory study on how well Sinovac protects people against the Omicron variant.
The study, spearheaded by Dr Malik Peiris and Dr David Hui, observed the production levels of virus-neutralising antibodies in the blood of individuals who had received two doses of the Sinovac vaccine in Hong Kong.
They have confirmed that the doses were insufficient to fight off the Omicron variant.
Sinovac had announced last week that 94 per cent of people who received three doses of its vaccine developed neutralising antibodies.
Nikkei Asia had reported Sinovac stating that its own lab study found that seven out of 20 people who had received two shots had tested positive for neutralising antibodies. So the efficacy rate would be 35 per cent. But the specific levels of neutralising were not revealed.
Researchers then tested the vaccine, setting it against a threshold of what they considered a sufficient level of antibodies for protection based on earlier studies published in the journal Nature Medicine, reported Bloomberg on Thursday (Dec 23).
With more than 2.3 billion doses of Sinovac already produced and shipped out across China and to many other countries, the Hong Kong study’s findings will be a blow to those who have already received the vaccine.
Sinovac has not responded to requests for a statement.
Meanwhile, the new study also showed that a booster shot of the Pfizer-BioNTech vaccine significantly improved the protection levels of those who had received two Sinovac shots.
A Pfizer booster will “achieve optimal protection against [the] omicron variant,” said Dr Peiris.
Booster shot introduction must be evidence-driven
In an interim statement on booster doses for Covid-19 vaccination, the World Health Organization said on Dec 22 that introducing the third dose “should be firmly evidence-driven and targeted to the population groups at highest risk of serious disease and those necessary to protect the health system”.
To date, the evidence indicates a minimal to a modest reduction of vaccine protection against severe disease over the six months after the primary series, the WHO noted. It added that the waning of effectiveness against all clinical disease and infections is more pronounced.
However, the duration of protection against the Omicron variant can be altered and is under active investigation.
“More data will be needed to understand the potential impact of booster vaccination on the duration of protection against severe disease, but also against mild disease, infection, and transmission, particularly in the context of emerging variants,” said WHO.
On Dec 1, Singapore’s Ministry of Health announced that those who had taken the second dose of the Sinovac or Sinopharm vaccines three months ago were eligible for the booster shot.
To maintain their fully vaccinated status from Jan 1, 2022, the individuals are strongly encouraged to take their third dose before Dec 31, 2021, said MOH. /TISG