Two doses of the Chinese-made Sinovac vaccine, one of the most commonly used jabs in China and around the world, provide “insufficient” antibodies against the Omicron coronavirus variant, according to researchers in Hong Kong.
The findings from a study released by the University of Hong Kong have stoked anxiety as Omicron surges in many parts of the globe and the first two cases were detected in mainland China this week.
China has administered more than 2.5bn doses of a Covid-19 vaccine — most of them Sinovac or Sinopharm — and adopted a “zero Covid” strategy that has subjected vast numbers of people to compulsory government quarantine. The new coronavirus strain had already raised questions over the efficacy of Chinese vaccines and Beijing’s ability to keep the virus under control.
“[Omicron] has left the Chinese vaccines even more ineffective against the threat posed by Covid,” said Nicholas Thomas, an associate professor at the City University of Hong Kong who specialises in Chinese foreign policy and health security in Asia. “The challenge for the Chinese authorities will be [to] re-engage their population’s commitment to another round of vaccines.”
The Hong Kong study tested the antibody levels of 25 people who received both doses of the Sinovac vaccine — an inactivated vaccine unlike messenger RNA jabs such as the shots developed by BioNTech/Pfizer — and found that none had sufficient antibodies in their blood serum to neutralise the new variant.
In contrast, five people out of a group of 25 who were given two doses of the BioNTech/Pfizer vaccine were found to have detectable neutralising antibodies against Omicron, which the researchers said had an “efficiency” of between 20 and 24 per cent against the new variant.
Last week Pfizer said that three doses of its jab would be able to neutralise Omicron based on a lab test.
Multiple laboratory studies have shown that the antibody protection provided by two doses of any vaccine is dented by Omicron. Separate preliminary studies from the University of Oxford and the Medical University of Innsbruck found that many double vaccinated Oxford/AstraZeneca recipients did not produce any measurable neutralising antibodies against Omicron.
The University of Hong Kong researchers said their study “demonstrated that both Omicron variants have reduced susceptibility to neutralisation by sera collected from Covid-19 vaccine recipients. None of the [Sinovac] recipients had detectable neutralising [antibodies] to the Omicron variants.”
A level of antibodies sufficient to neutralise the virus is closely related to the ability to prevent symptomatic infection, previous studies have shown. However, experts stress that double vaccinated people will still retain some protection against severe disease because this is mediated by T cells and B cells rather than antibodies.
Kevin To, one of the HKU researchers, told the Financial Times that data on a third Sinovac dose “would be needed” to determine whether those who have had two Sinovac jabs should switch to other vaccines for the booster shot.
David Hui, a Hong Kong government pandemic adviser from the Chinese University of Hong Kong, said another study was under way on a three-shot course of the Sinovac vaccine to protect against Omicron. The findings are expected to be published next week.
Huge populations in countries including Turkey, the Philippines and Indonesia have received the Sinovac vaccine. Sinovac, which said on Wednesday its own lab test results showed a third dose could effectively improve the ability in neutralising Omicron, was not immediately available for comments on the study.
Nine Omicron cases were recorded in Hong Kong as of Wednesday, just as final preparations for resuming quarantine-free travel to mainland China were being carried out. A top adviser to city leader Carrie Lam dismissed concerns raised by the study.
“For the time being, Hong Kong is using a zero Covid strategy to prevent infection . . . so no worries yet,” Lam Ching-choi, a medical doctor and a member of Lam’s de facto cabinet, told the FT. “[Omicron] has not [affected border reopening plans] for the time being . . . The Omicron cases were well contained, [with] no [cases] being spread into the community.”
Additional reporting by Oliver Barnes in London
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