Replying to media questions yesterday, the top microbiologist from the University of Hong Kong, who is fully vaccinated, thanked people for their concern but said he had not fallen ill and has been staying at home as instructed by authorities.

"It's a good thing that I can enjoy several days off after three years," he said.

Yuen last attended a public event on August 31, when he shared anti-Covid experiences with representatives of the property sector in a seminar.

His HKU colleague, infectious disease expert Ho Pak-leung, said he met Yuen on Tuesday.

"Yuen was in good spirits and his voice was loud and clear," he said.

Ho said Yuen, being fully vaccinated before his infection, believes he can recover soon, adding a long-Covid bout is unlikely.

For his part, Deputy Chief Secretary Warner Cheuk Wing-hing, infected on August 26, is still testing positive, prompting him to say the virus is "very cunning,"

Cheuk had a high fever and severe coughing at first, then tested negative five days after the infection but turned positive again this week.

The news about Yuen and Cheuk came as the quota for SAR travelers to Shenzhen will go down by half to 1,000 from Monday as it conserves resources to fight outbreaks.

According to Shenzhen's online booking system, the quota will first be trimmed from the present 1,800 to 1,500 on Sunday before hitting 1,000 on Monday. The cuts come as the city of more than 17 million saw 25 cases on Wednesday.

Legislative Council member Kingsley Wong Kwok believed people are less likely to head north because of the worsening Covid situation there, adding the urgent travel needs of students studying in mainland schools had already been taken care of.

He said just thousands are applying for the quota of late - much lower than the 10,000 to 20,000 daily applications earlier.

He urged the mainland and the SAR to implement as soon as possible the "reverse quarantine" arrangement, which allows Hongkongers to undergo quarantine in the SAR before crossing over to the mainland.

The mainland also announced yesterday that everyone catching flights, high-speed railway, trains and other interprovincial public transport must present a negative PCR test result within 48 hours.

That came as Hong Kong saw 11,091 cases - 10,910 local infections and 181 imported cases, and 12 deaths.

Reports of 1,356 cases came in from 777 schools, involving 1,163 students and 193 staff.

A total of 24 schools saw classes with outbreaks being suspended for a week.

Five care homes - three for the elderly and two for the disabled - saw 15 cases.

The Central Kowloon Health Centre in Kowloon City will become the eighth designated Covid-19 clinic starting today.

The Hospital Authority said 1,178 patients visited designated clinics over the past two weeks and 1,051 used its remote medical consultation services.