A government pandemic advisor, David Hui, said on Sunday that the current flu outbreak may have already peaked.

He said based on Hospital Authority lab figures, case numbers may have reached the peak between April 15 and 19 and have been gradually coming down, but he stressed there is a need to observe figures from Department of Health labs.

Hui said after the mask mandate was lifted at the start of March, the flu outbreak began at the start of April.

On a TVB programme, he noted that flu outbreaks normally take four to six weeks to reach its peak, but this time, it may have only lasted around two to three weeks.

"The main reason why it's peaked quicker is that, number one, quite some people have been vaccinated. Also, the temperature now is higher than 20 degrees Celsius, the flu is normally more active when it's below 20," Hui said.

"We also see in the community that many people are still wearing masks. So with these factors, it seems the flu outbreak may not be a very big one."

The Chinese University professor said H1N1 is the current dominant flu strain, similar to those in the past, and the elderly and children are most affected.

He said it is hard to predict how a summer flu outbreak here will materialise because that depends on a number of factors, including how bad the outbreak may be in Australia and New Zealand, which are entering winter.

Hui said for Covid, it is not a surprise that there has been a rebound in infections as some people are no longer wearing masks.

He said much like in Singapore and India, most of those infected in Hong Kong are suffering from mild symptoms.

But the respiratory medicine professor called on high-risk groups to get a Covid booster around six months after their last shot or infection, saying their antibodies may have waned.