Officials at the Centre for Health Protection said on Wednesday that vulnerable people should get vaccinated as soon as possible as the winter influenza season has begun, a week earlier than last year.

The centre’s controller Dr Wong Ka-hing said flu cases are expected to increase in the coming weeks. He urged vaccinations for children, the elderly and patients with chronic diseases and for people to observe strict personal hygiene, according to a government release.

Wong said the peak flu season could last for 14 to 16 weeks and that it takes about two weeks for antibodies to develop in the body after people get the flu vaccine.

So far this winter, more than 80% of cases have involved the influenza A(H1) virus, with children and adults aged from 50 to 64 years slightly more affected.

About 20% of the cases involved the influenza A(H3) and very low influenza B activity.

Over the past four weeks, 341 people were affected by influenza-like illnesses in kindergartens, childcare centers and primary schools, it said. But that number is expected to increase when classes resume after the Christmas and New Year holidays.

Some 960,000 flu jabs have been given and the vaccination rate has increased significantly compared to last year.