Flu ｜ Two children still developed severe illness after receiving vaccines. Au Ka-wing: Immunity declines over time about half a year after vaccination, and those who got the shots still have fewer severe cases.

Hong Kong has officially entered the summer influenza peak season. When asked whether Hong Kong needs to adjust the vaccination frequency after two children contracted Influenza A despite being vaccinated, with one in critical condition, the Centre for Health Protection stated today (2nd) that vaccine efficacy gradually declines six months after vaccination, but according to WHO recommendations, only one dose per year is needed. It also emphasized that the rate of severe complications in vaccinated children is more than five times lower than in unvaccinated children, urging parents to get their children vaccinated as soon as possible.

Earlier this week, the centre reported two severe influenza cases in children, both of whom had received the 2025/26 seasonal influenza vaccine. When asked whether the vaccine efficacy was insufficient against the current circulating virus and whether an earlier booster dose was necessary, Dr. Albert Au, head of the Communicable Disease Branch of the centre, stated that the two patients were vaccinated between October and November last year. Scientifically, immunity is strongest in the six months following vaccination and gradually declines over time, so revaccination is needed the following year.

Influenza | Vaccine effectiveness in preventing hospitalization still reaches 40-60%

However, he emphasized that during the winter influenza peak from November last year to January this year, the rate of severe illness or complications in vaccinated children aged 6 months to 17 years was significantly lower than in unvaccinated patients, with a relative risk difference of 5.3 times. This reflects that the influenza vaccine effectively prevents severe complications after influenza infection, with a hospitalization prevention efficacy of 40-60%.

Dr. Leung Yiu-hong, head of the Emergency Response and Project Management Division of the centre, added that the government has administered over 2.03 million doses of influenza vaccine cumulatively, with an overall influenza vaccination coverage rate of about 65% among children, more than two percentage points higher than the same period last year. However, the coverage rate for children aged 6 months to under 2 years is currently only 27%, lower than other pediatric age groups, urging parents to get their children vaccinated as soon as possible.

Influenza | Still following WHO recommendations, no plans to purchase both Northern and Southern Hemisphere vaccines simultaneously

Regarding whether the changing seasonal pattern of influenza necessitates following Singapore's approach of purchasing both Northern and Southern Hemisphere influenza vaccines to ensure year-round vaccination, Dr. Au explained that most regions and countries in the Northern Hemisphere typically experience their winter influenza peak from November to March. WHO recommends vaccination before the peak season, so vaccines start becoming available in August and September on the market. The Southern Hemisphere, conversely, enters its winter influenza peak from April to July.

Dr. Au pointed out that it is not possible to purchase both Northern and Southern Hemisphere vaccines simultaneously because their market release times differ. Since Hong Kong is in a subtropical region, WHO recommends using Northern Hemisphere vaccines. The centre also advises the public to get vaccinated against influenza in October each year. He emphasized that WHO recommends only one influenza vaccination per year, and vaccine effectiveness generally lasts from six to nine months.

Influenza | Emergency department visits decreased by 40k after fee reform

Regarding the assessment of emergency department patient flow during the winter influenza peak after public hospitals implemented fee reform this year, Dr. Lee Lap-yip, General Manager (Cluster Operations) of the Hospital Authority, stated that emergency department visits have remained at a high level recently, with some days exceeding 6,000 visits. However, as of the 28th of last month, total emergency department visits were about 900k, compared to 940k during the same period last year. Among these, semi-urgent and non-urgent patients decreased from 510k last year to 450k this year, reflecting a reduction in visits for relatively mild conditions, likely related to the fee reform.