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Health authorities in China have detected a second case of the Omicron coronavirus variant, and a new study suggests the most widely used vaccine in the country may not offer sufficient protection without a booster shot.

China has one of the world’s strictest quarantine regimes, and both cases – in the cities of Tianjin and Guangzhou – were detected while travellers were undergoing mandatory isolation and testing. But while this provided some validation for the country’s “zero COVID” approach, news out of Hong Kong may leave officials highly concerned.

According to a study by researchers at Hong Kong University, to be published in the medical journal Clinical Infectious Diseases, initial lab findings show that two of the most widely available vaccines “do not produce sufficient levels of serum antibodies against the new Omicron virus variant.”

The team examined samples from two groups of 25 people who had received two doses of either Pfizer-BioNTech’s shot or Sinovac’s CoronaVac. Only five of the Pfizer-BioNTech vaccine recipients could produce antibodies that neutralized the Omicron variant, while none of the Sinovac subjects could do so.

In a statement, the HKU researchers said Omicron “was able to reduce the effectiveness of two doses of COVID-19 vaccine, particularly against CoronaVac.

“Therefore, COVID-19 vaccine recipients or even those recovered COVID-19 patients may be at a higher risk of breakthrough or reinfection,” they said. “Our findings suggest that the design of the next generation of COVID-19 vaccine should consider sufficient coverage against this novel viral variant.”

The team recommended people receive a third dose to “enhance the antibody response against the Omicron variant,” while noting that “whether a third dose of the present CoronaVac vaccine will enhance the neutralizing antibody response against the Omicron variant remains to be determined.”

Sinovac, a Chinese pharmaceutical company, released its own Omicron trial data Wednesday, after the HKU study, saying that of 20 samples tested, seven showed sufficient antibodies to neutralize the variant.

CoronaVac is the most widely used vaccine in China and around the world, approved for use in dozens of countries, according to Sinovac. More than 2.3 billion doses have been shipped worldwide, the company said, and more than 1.9 billion have been administered. If the current two-dose regimen is found to be ineffective against Omicron, it could set back global vaccination efforts and delay a return to normal in many countries as they roll out millions of booster shots.

The good news is that booster shots do seem to be effective against the new variant. Last week, Pfizer-BioNTech said lab testing showed just that, while Sinovac’s own research has shown similar results, with as much as 94-per-cent efficacy after a third dose. Another Chinese pharmaceutical company, CanSinoBIO, said testing showed a third dose of its inhaled vaccine, in combination with two shots, was also effective in neutralizing Omicron, state media reported Tuesday.

Booster shots will take time to roll out, however, raising the potential for a spike in cases as Omicron spreads. China in particular could be at risk because the effectiveness of the country’s strict pandemic policies means there is little natural immunity to the virus among the population. Earlier this year, there were multiple small outbreaks caused by the highly transmissible Delta variant.

As well as an onerous 21-day quarantine for international arrivals, even minor outbreaks within China have seen millions of people placed under lockdown and subjected to mandatory testing. While this approach has proved successful at controlling the spread of infections, it has led to widespread misery in some border areas, where preventing the virus from entering the country is a daily battle.

Chinese officials have stridently defended the country’s approach, and reversing course at this stage could be disastrous: A recent study by researchers at Peking University found that were China to lift its pandemic controls and pursue a “living with COVID” strategy similar to those of many other countries, it “would have a devastating impact on the medical system of China and cause a great disaster within the nation.”

Within days, the researchers said, the number of cases would rise into the hundreds of thousands, while the number of severe cases would exceed the country’s peak of 11,977 reached in February, 2020, near the start of the pandemic, “and thus would pose an unaffordable burden to the medical system in this country.”

“More efficient vaccinations or more specific treatment, preferably the combination of both, are needed before entry-exit quarantine measures and other COVID-19 response strategies in China can be safely lifted,” they concluded.

China is nearing a milestone that experts said would enable a slow relaxing of restrictions: a vaccination rate of 83 per cent, which health officials said should provide herd immunity.

At a news conference Saturday, however, officials from the National Health Commission warned the new variant may change things, particularly if current vaccinations prove less effective in preventing serious illness.

“Omicron has further increased the uncertainty of the pandemic,” NHC spokesman Mi Feng said.

Alexandra Li contributed to this report

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