Hong Kong health officials confirmed on Thursday that a mutated influenza A (H3N2) virus strain is circulating in the city and that the second pediatric death of the current flu season has now occurred.

The latest fatality involves an eleven-month-old boy who succumbed to flu-associated complications in recent days.

The Centre for Health Protection sounded the alert after experts observed that the novel strain has rapidly replaced the previously dominant H3N2 virus according to laboratory surveillance during the past two months.

“The proportion of the mutated virus strain is rising, and is replacing the [previous] strain,” said Professor David Hui Shu-Cheong of the Chinese University of Hong Kong.

The Department of Health noted that the World Health Organization expects this mutated strain to dominate in the 2025-26 Northern Hemisphere season.

Despite the mutation, authorities emphasised that the existing seasonal influenza vaccine remains effective in reducing the risk of severe disease, hospitalisation and death, even though protection against mild infection may be diminished.

The health department called on parents and eligible risk groups to receive vaccination promptly and stressed that children aged six months and above—except those with contraindications—should be immunised.

Clinicians and public-health officials are also warning that children and infants without prior exposure or vaccination appear particularly vulnerable.

The city has already seen multiple severe pediatric flu cases this year, and the emergence of the mutated strain raises concern for heavier burden during the lead-in to the winter flu season.

In response, authorities launched enhanced surveillance, urged public-place mask use for symptomatic individuals, and advised care-home residents and families to maintain strict hygiene.

Parents are encouraged to seek immediate medical attention for children presenting prolonged fever, joint pain, cough or rash—especially if they have not been vaccinated.

The Department of Health emphasised that timing remains critical: vaccination should be sought ahead of peak influenza activity, which may arrive earlier than in prior years.

While the new strain drives increased attention, officials caution against alarm, reinforcing that vaccination, hygiene, prompt care and antiviral treatment remain the best defence.

Health systems are preparing for higher patient loads, particularly among young children, and emphasise that even those with good past health can face serious complications from influenza.

The mutated H3N2 spread underscores the need for proactive public health responses ahead of the worst of this season’s respiratory-virus wave.