An infectious diseases expert said on Saturday the winter influenza season was showing signs of peaking in Hong Kong, with more flu cases being logged in December.

Speaking on a radio programme, Ivan Hung, clinical professor at the University of Hong Kong, said numbers from the Centre for Health Protection showed influenza activity had started to pick up in September, with the dominant strain being Influenza A virus subtype H3N2 and October seeing a slight peak with a positivity rate of around 10 percent .

The number came down slightly in November but rebounded in December to around 7 percent, he said.

"When we enter the Lunar New Year in January and February, with the cold weather, I believe the winter flu will break out and infections will increase," Hung said.

"This will continue until after the Lunar New Year, around March when the weather becomes warmer and immunity rates in the community are high enough, then the peak flu season will start to decline," he added.

Hung said getting vaccinated against flu is crucial to preventing severe cases of influenza, especially when schools resume after holidays, and the cold weather favouring virus replication.

He said vaccination rates were satisfactory in the past few months, with nearly 70 percent of primary school students and more than half the elderly getting the flu jab.

But the professor urged those aged 18 to 50 to get jabbed as soon as possible, due to low vaccination rates among the age group.