The Post outlines what you need to know about the latest flu infections, including how serious they are, who is most vulnerable and how to minimise risk.

1. How serious are flu infections in the city?

The latest statistics from the Centre for Health Protection showed 47 people came down with severe flu between April 9 and 15 and that 20 of them had died.

Among the serious cases, 14 of them, about 30 per cent, had been vaccinated against the illness.

The number of serious cases marked a 74 per cent increase from the 27 recorded in the first week of the month.

Another 29 serious cases were logged between Sunday and Wednesday this week, 17 of which were fatal.

Since the start of the flu season on April 6, 103 people have developed serious conditions, and 49 of them have died.

“It’s on the rise. Lack of exposure over the past three years due to social-distancing measures lowered our immunity,” Professor David Hui Shu-cheong, a respiratory medicine specialist at Chinese University, said.

He added that the removal of the mask mandate in March had contributed to the present outbreak.

2. When will infections peak?

Different indicators for flu activity continue to show an upwards trend, including the rate of influenza-like illnesses in public and private clinics, the number of flu-positive samples handled by the public laboratory, and public hospital admissions associated with the illness.

Respiratory medicine specialist Dr Leung Chi-chiu said the peak of infections was in January and February in normal conditions, but the strict social distancing rules and mask requirement imposed for Covid-19 had led to a delayed 2023 flu season.

He said infections started to rise six weeks ago and could peak in one to two weeks based on the present rates, but added that the level might not be as high as those recorded pre-pandemic.

“The relatively warmer temperatures, the masking, and the flu vaccination coverage mean that the situation this year may not be very serious,” he explained.

3. Who are most at risk?

The elderly and children are particularly vulnerable to flu infections and its complications, medical experts said.

Professor Lau Yu-lung, from the University of Hong Kong, said most the serious flu cases involved children, as well as the elderly, who had weaker immunity and organs and usually had chronic illnesses.

Lau warned that flu infection could lead to acute brain damage in children under five years old.

Dr Wilson Lam, the vice-president of the Hong Kong Society for Infectious Diseases, said flu infections had rebounded significantly this year.

He said most of the serious and fatal cases involved elderly people and most deaths were among those with chronic diseases or unvaccinated, who could develop complications.

20 deaths among 47 serious flu cases spark warning to Hong Kong public to get jab

4. How to minimise risks?

Doctors maintain vaccination is one of the most effective ways to prevent flu infection and its complications, as well as reduce related hospitalisations and deaths.

Wearing masks and keeping hands clean can also help, experts said.

The government recommends that everyone aged 6 months or above, except those with known contraindications, should get seasonal influenza vaccinations.

People, especially the elderly and children, are advised to get the jab early as it takes about two weeks to develop antibodies.

Lau, chairman of the Scientific Committee on Vaccine Preventable Diseases, said years of anti-Covid-19 measures such as wearing masks and regular handwashing had weakened people’s immunity, as the city had not experienced surges in flu cases in the three years since the Covid-19 pandemic began.

The last flu season in Hong Kong ran from late 2019 to early 2020.

“The public in the past three years did not have a chance of getting infected,” Lau said. “If people got vaccinated, they could develop some immunity.”

Hongkongers urged to up vigilance against flu after ‘slight’ infection spike

The priority groups for vaccination include healthcare workers, people aged 50 or older, pregnant women, care home residents, those with chronic illnesses and children aged six months or older, recommendations on flu vaccination issued by the scientific committee on Wednesday said.

Lam said vaccination might not guarantee infection prevention, but it could reduce the risk of severe illnesses, especially for the priority groups.

About 1.5 million doses of seasonal influenza jabs had been administered through the government’s vaccination programme and the vaccination subsidy scheme by March 19.

The vaccination coverage rate for people aged 65 or above reached 47 per cent and that for children aged up to 18 was nearly 40 per cent.

The coverage rate for toddlers aged 6 months to two years old was about 8 per cent.