Some 322 serious flu cases have been reported since January, the Centre for Health Protection said.

Controller Dr Leung Ting-hung said there was still a high number of serious cases. "The flu surge will remain for some time," Leung said, after meeting the centre's vaccine committee.

But fewer patients have tested positive for flu in laboratory checks this week. The percentage fell from 34 per cent last week to about 30 per cent this week.

Health officials said those most susceptible would be given the H3N2 vaccine first when it arrived in the city. Dr Chow Chun-bong, chairman of the vaccine committee, said: "Most deaths are elderly patients, aged 85 or above … so we'll give priority for the vaccine according to age."

Leung noted that it was necessary to give priority because the vaccine supply was limited.

"Originally these vaccines were destined for the southern hemisphere. Supply for the northern hemisphere is limited," Leung said. He added that the stocks due to arrive in April would not be enough to meet demand in the city.

Medical staff would be a lower priority, since there was not a huge problem with outbreaks in hospitals. "Health-care workers are not considered to be among the high-risk group," Chow said. But people working in aged-care homes or intensive care units would be encouraged to get vaccinated, he said.

Chow also said that another flu surge was expected in summer, but on a smaller scale.

And health minister Dr Ko Wing-man warned that the current outbreak was not over yet, even if there were fewer people testing positive for the flu virus.

"The drop in positive samples could be because more people are leaving the city for the holiday," said Ko after inspecting the Prince of Wales and Tuen Mun hospitals yesterday to assess how well prepared they were for the Lunar New Year break. Ko urged hospitals to prepare for more patients when people returned from holiday, when wards were likely to fill up again.