He said yesterday cases hit 5.8 percent of those tested for influenza recently and the peak could last for weeks.

Although most patients only had mild symptoms, high-risk groups - the elderly, the chronically ill and those who are expecting - might develop serious illnesses or even die following an infection, he said.

Lam said we usually see flu peak in winter and summer, with many serious cases detected in January and February.

"Due to the pandemic, the peak season for flu in 2020 was shorter. In 2021 and last year, the virus even seemed to disappear," Lam said, adding that the SAR was now seeing "an obvious rebound."

As the flu virus did not spread widely during the pandemic's duration, people have lower immunity against it, causing the rebound, he said.

"A similar rebound of flu cases was also seen overseas," Lam said, adding that the number of infections around the world was higher compared to previous years.

"With the pandemic coming to an end, people have resumed life as normal while social-distancing measures have also been lifted," he said.

Lam's comments came as the Centre for Health Protection reported a case of severe pediatric influenza A infection Monday, involving a 17-year-old with cerebral palsy, which affects one's ability to move and maintain balance and posture.

The teenager had a fever and shortness of breath starting Sunday and was admitted to North District Hospital in a critical condition. He was later transferred to the Prince of Wales Hospital and was found to have an influenza A infection complicated by pneumonia and shock.

He did not get a seasonal flu vaccine and two of his family members also had upper respiratory tract infections recently.

Lam also warned about a possible Covid-19 rebound as the viral load detected in sewage samples was still high, saying "the coronavirus has never left the Hong Kong community."

But he said people do not have to worry because the number of severe infections and deaths remained at low levels and most people would only have mild symptoms.