Currently citizens should wait six months after taking their second dose to get a booster jab, but Hui said experts will discuss whether to shorten the period due to the Omicron threat during their next meeting on December 23.

“Before the emergence of the Omicron variant, BioNTech takers can wait for more than six months to get a booster shot because their antibody level drops slowly,” Hui said on a radio program on Monday.

“But as the Omicron variant, which can reduce vaccines’ efficacy, is spreading across the world, the interval between the second and the third shot may be shortened,” he said.

Hui said overseas studies have shown that a third BioNTech shot can protect people from the new Omicron variant. But there is no data on how the new variant affects the Sinovac vaccine, he said.

Although some pharmaceutical companies are developing new vaccines that target the Omicron variant, Hui said Hongkongers should not wait for new vaccines.

“Even if the companies can produce the second generation vaccines within a short time, they still need to conduct clinical trials and cannot launch the vaccines immediately,” Hui said.

The latest Omicron variant was first detected in Botswana and South Africa in November, and it has now spread to more than 60 countries.

In the United Kingdom, Prime Minister Boris Johnson has accelerated the booster program because scientists did not yet know if Omicron is less severe than other variants.

"A tidal wave of Omicron is coming," Johnson said on Sunday. "And I'm afraid it is now clear that two doses of vaccine are simply not enough to give the level of protection we all need."

"Everyone eligible aged 18 and over in England will have the chance to get their booster before the New Year," he said.

The Covid booster program in Hong Kong opened to over 30s today, and all adults who had their second vaccine at least three months before can book a booster jab from Wednesday.