High number of paediatric cases recorded in ongoing influenza season

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25th April 2024 – (Hong Kong) According to the latest data released by the Centre for Health Protection (CHP) of the Department of Health, the local seasonal influenza activity in Hong Kong remains at a high level, and it is expected that the current influenza season will continue for some time. The CHP has once again urged the public to remain vigilant, emphasizing that individuals belonging to high-risk priority groups, especially children, should receive the seasonal influenza vaccination (SIV) as soon as possible to prevent severe illness and fatalities.

Since early January this year, Hong Kong has been experiencing the current influenza season. The most recent surveillance data, up until the week ending 20th April shows that the majority of positive detections during this period were influenza A(H1) viruses, accounting for approximately 83% of the cases. This indicates a shift from the previously dominant influenza A(H3) strain observed from January to March. The admission rate for influenza-related cases in public hospitals remains high, with 0.69 cases per 10,000 population. The latest statistics from the Public Health Laboratory Services Branch of the CHP and Hospital Authority (HA) indicate that 9.76% of respiratory specimens tested positive for seasonal influenza viruses, signifying a significant level of infection. Additionally, there has been a notable increase in the number of influenza-like illness outbreaks in schools and institutions, with 29 outbreaks recorded as of the week ending April 20, compared to around 10 outbreaks per week in the first half of April. In relation to this influenza season, a total of 20 paediatric cases of influenza-associated complications or deaths have been reported, including two fatal cases. Alarmingly, 15 of these cases had not yet received the 2023/24 SIV.

In Hong Kong, the seasonal influenza virus strains detected include influenza A(H1), influenza A(H3), and influenza B viruses, which typically exhibit heightened activity during influenza seasons. Normally, the influenza season lasts for eight to 12 weeks; however, the duration can be prolonged when there is a transition in the dominant virus strain. For instance, during the 2015/16 winter influenza season, influenza A(H1) initially dominated but was eventually surpassed by influenza B, resulting in a prolonged season lasting about 16 weeks with more severe cases. This season, the CHP has observed a gradual shift from influenza A(H3) to influenza A(H1) as the predominant strain. It is anticipated that the current influenza season will persist for a significant period, potentially leading to more outbreaks and severe cases in the coming weeks, according to a spokesman for the CHP.

The CHP has also continued its surveillance of other respiratory pathogens. Recent data, as of 20th April, revealed that rhinovirus/enterovirus activity remained the highest among children, accounting for 22% of respiratory specimens received by the HA. Adenovirus was the next most active pathogen, with a positive percentage of 8.6%. Furthermore, the proportion of children testing positive for Mycoplasma pneumoniae infection has increased from approximately 5% two months ago to 8% currently. Other respiratory pathogens, including respiratory syncytial virus, human metapneumovirus, and parainfluenza viruses, accounted for 6.7%, 5.5%, and 3.5% respectively.

The spokesman reiterated that various respiratory pathogens, including the influenza virus, can be transmitted simultaneously. It was emphasized that vaccination is a safe and effective preventive measure against seasonal influenza. The Scientific Committee on Vaccine Preventable Diseases under the CHP has stated that the SIV is effective against influenza A (including H1 and H3) and B. The CHP strongly recommends that members of the public who have not yet received the SIV, particularly high-risk groups such as young children, the elderly, and individuals with chronic diseases, should prioritize vaccination without delay.