Over the past two weeks, the Centre for Health Protection has recorded 1,130 infections in children below three years, compared with 874 in the age group the previous fortnight.

The Hospital Authority said the boy no longer required the use of a breathing machine and had improved from critical to stable condition, but he remained in the pediatric intensive care unit at Princess Margaret Hospital for close monitoring.

Meanwhile, a five-year-old girl with brain inflammation triggered by Covid remained in critical condition in the pediatric intensive care unit at Tuen Mun Hospital.

Cochairman of the authority's coordinating committee on pediatrics, Alan So King-woon, said public hospitals have admitted twice more children with Covid compared with last month. A higher proportion of them have serious symptoms such as fever.

"Children have poor immunity and immature body functions. When they're sick, their conditions may take a turn for the worse much quicker than adults," So said. "The situation is worrisome as school [is about to start]. Children have not gone to school for some time and they'd be very happy to see their friends again. It's inevitable that there will be hugging and cuddling. It's hard to do infection control."

Covid adviser Lau Yu-lung said hospitals have recorded more than 30 patients suffering from croup over the past month. But he said the cause might not be related to the patients' high viral load.

"Two three-year-old kids can have completely different reactions [to the infection]. We believe some personal factors exist," Yau told a radio program. "What we can do is get our children vaccinated."

He added: "Parents should not assume the medical system can handle serious illnesses and that kids can completely recover upon receiving sufficient treatment in intensive care.

"The more serious the illness is the less likely it is to fully recover from."

As of yesterday, 4,576 toddlers aged six months to three years have taken at least one jab.

Lau said with the current vaccination rate in the age group, the coverage can reach 40 percent in December, but he wished the daily inoculation number can be pumped up to 600 to reach 60 percent rate by yearend.

Separately, health authorities reported 11 deaths yesterday, taking the city's toll since the fifth wave began to 9,356.

The latest fatalities were seven men and four women, aged 60 to 97. Among them, an 86-year-old man died at home. Of the 10 who died in public hospitals, seven had not been fully vaccinated with three doses.

One of the fatalities was 60-year-old man receiving chemotherapy for lung cancer. He tested positive in a rapid test at home on Thursday, but did not report his infection.

He consulted the North District Hospital accident and emergency ward on Sunday for cough and shortness of breath, but passed away the same day.