The Health Bureau gazetted the extension of compulsory mask-wearing in all pubic venues and on transport on Wednesday night.

Although citizens urged authorities to keep up with overseas countries and scrap the mask mandate as soon as possible, respiratory expert Leung Chi-chiu told The Standard the Covid-19 viral load detected in sewage remained at a high level yesterday.

"As the SAR is relaxing other social distancing measures it is better for us to continue to wear masks for a while," Leung said.

"If the government believes the healthcare system is not facing pressure it can soon scrap the mask mandate at outdoor places without huge crowds," he added.

The administration announced earlier a cancellation of the daily rapid test requirement for secondary school students starting next Wednesday, March 1.

The test mandate for primary and kindergarten students remains until March 15.

Leung also said the administration could consider scrapping the indoor mask mandate at the end of March if there are no large-scale outbreaks at schools after lifting test requirement for all students.

"Hong Kong is one of the few places with mask mandates because it was hit by the pandemic later than other countries and relaxed restrictions slower," he said.

"Therefore, people from other countries may wish Hong Kong to scrap all measures as soon as possible. However, we still need to protect vulnerable groups,"

Leung also warned of the risk of flu transmission after the mask requirement is lifted, noting that seasonal flu hit Western countries quickly after people took off their masks.

"In the winter of 2018 and 2019 when there were no anti-Covid measures there were a lot of severe flu cases among young patients and the admission rate was high," he added. "The number dropped to a low level after people started wearing masks for Covid.

"Children aged below three, who have never been exposed to the flu and are not vaccinated, are at high risk and parents should take them to get the jab as soon as possible."

Government adviser Ivan Hung Fan-ngai also said Hongkongers have a weaker immunity against the flu as well as other upper respiratory tract infections due to limited exposure over the past three years.

He suggested authorities lift the mask mandate in warmer weather when the flu viruses are less active.

But the Hong Kong Committee on Children's Rights urged authorities to drop the mask rule as soon as possible as young children could not learn how to communicate properly among people with face coverings.

But Leung said some unpopular rules have to be imposed to protect high-risk groups.