Respiratory health expert David Hui on Sunday warned that although the number of flu infections in Hong Kong has been dropping for several weeks, there could be a rebound in cases at any time.

On a radio programme, the Chinese University professor said cold weather expected over the Lunar New Year period could lead to a surge in people coming down with the virus.

He urged those infected to wear masks and not to go to work or school if they have symptoms.

Hui said the latest influenza jab is effective.

"Because the vaccine right now is a four in one which covers H3N2, H1N1, and two types of influenza B, the outbreak will be relatively lower with a high vaccination rate. This year, the situation is handled well because 80 percent of people in elderly homes have had their vaccination. Overall, the vaccination rate is a little higher than before," he said.

"The only drawback is that the vaccination rate for those who are 65 years and older is only 49.4 percent, meaning over a half haven't had it yet. These high-risk individuals should definitely be vaccinated."

On Covid-19, the professor said the situation in the territory has been relatively stable of late. However, there are about 460 people currently in hospital with the illness, and there have been some severe cases and deaths recently, he said.