Hong Kong entered its winter influenza season in January, meaning flu activity is expected to rise in the coming months. For the elderly and those with weaker immunity, contracting the flu can lead to severe illness, potentially causing complications like bronchitis, pneumonia, encephalopathy, and even death. In past severe or fatal flu cases, approximately 70% of patients had not received the seasonal flu vaccine.
The Centre for Health Protection reminds the public that vaccination is the most effective way to prevent influenza and its complications. The government also provides corresponding subsidy schemes, offering free or subsidized flu vaccination for eligible individuals.
Why Get the Seasonal Flu Vaccine?
The flu vaccine provides protection against influenza. Even healthy individuals can develop severe flu. Therefore, it is recommended that all individuals aged 6 months and above (except for those with specific known contraindications) receive the seasonal flu vaccine annually to protect their health. Young children, the elderly, and individuals with chronic illnesses are particularly encouraged to get vaccinated as soon as possible.
Who is Eligible for Free or Subsidized Vaccination?
The 2025-26 Seasonal Influenza Vaccination Program began on September 22, 2025. To encourage vaccination, the government provides free or subsidized seasonal flu vaccination for the following eligible groups:
- Individuals aged 50 or above (general population or those with chronic illnesses).
- Pregnant women.
- Individuals aged 18-49 with chronic illnesses, or eligible individuals with intellectual disabilities or disabilities.
- Children aged 2 to under 18 (general population or those with chronic illnesses).
- Infants aged 6 months to under 2 years.
- Residents of residential care homes for the elderly, residential care homes for persons with disabilities, and residential child care centres.
- Public healthcare staff and staff of residential care homes.
- Personnel in the poultry industry, pig farming, and pork slaughtering industries.
Where to Get Vaccinated?
The government has opened all 29 Department of Health Maternal and Child Health Centres for vaccination of all children aged 6 months to under 2 years. Other locations include:
- All 18 District Health Centres (DHCs) and DHC Expresses under the Primary Healthcare Office.
- The 74 Family Medicine Clinics and 38 public hospitals under the Hospital Authority.
Citizens can also use the eHealth website to find a list of private doctors enrolled in the Vaccination Subsidy Scheme (VSS).
Trivalent vs. Quadrivalent Vaccines: What's the Difference?
Both are effective and safe in preventing flu and related complications, hospitalization, and death.
- Trivalent Vaccine: Contains antigens for two influenza A strains (H1N1 & H3N2) and one influenza B strain (Victoria lineage).
- Quadrivalent Vaccine: Contains antigens for two influenza A strains (H1N1 & H3N2) and two influenza B strains (both Victoria & Yamagata lineages).
Types of Vaccines: Inactivated, Recombinant, and Live Attenuated
Three types are recommended for use in Hong Kong:
- Inactivated Influenza Vaccine (IIV - Injection): Contains killed virus. Suitable for individuals aged 6 months and above (some brands for 3+), including those with chronic health conditions. Recommended for children with conditions like asthma.
- Recombinant Influenza Vaccine (RIV - Injection): Made using recombinant technology without eggs or live flu virus. Suitable for individuals aged 18 and above. If available, elderly residents of care homes should be prioritized for this vaccine, which may offer them better protection.
- Live Attenuated Influenza Vaccine (LAIV - Nasal Spray): Contains weakened live virus. Recommended for healthy, non-pregnant individuals aged 2-49 who are not immunocompromised. Note: The weakened virus may potentially be transmitted to immunocompromised individuals.
Possible Side Effects
- Inactivated & Recombinant Vaccines: Common local reactions include pain, redness, and swelling at the injection site. Some may experience fever, chills, muscle aches, and tiredness.
- Live Attenuated Vaccine (Nasal Spray): Side effects may include mild runny/stuffy nose, low-grade fever, and sore throat.
Side effects are usually mild and short-lived. Consult a doctor immediately if you experience persistent fever, severe allergic reactions (difficulty breathing, swelling of mouth/tongue, hives), or other concerning symptoms post-vaccination.
Safety for Pregnant/Breastfeeding Women & Infants
- Pregnant Women: Vaccination is recommended for all pregnant women to reduce the risk of acute respiratory infection and hospitalization for both mother and baby. Note: LAIV (nasal spray) is NOT suitable for pregnant women.
- Breastfeeding Mothers & Infants: Seasonal flu vaccines are safe. Antibodies produced by the vaccinated mother can be passed to the infant through breast milk, providing some protection.
How Long Until It's Effective?
It takes about two weeks after vaccination for the body to develop protective antibodies. Get vaccinated early to be protected before the flu season peaks.
Why Get Vaccinated Every Year?
- Declining Immunity: Antibody levels from vaccination decline over time.
- Changing Viruses: Circulating flu virus strains change constantly. Vaccine composition is updated annually to match the predicted prevalent strains for better protection. According to the US CDC, when the vaccine is well-matched, it can reduce the risk of flu illness by 40-60% in the overall population.
Why Might Someone Still Get Sick After Vaccination?
- Two-Week Window: Infection can occur within the two weeks it takes to build immunity.
- Vaccine Side Effects: Side effects like fever or muscle aches can be mistaken for flu.
- Other Viruses: Other respiratory viruses (causing colds, etc.) can produce flu-like symptoms.
- Vaccine-Virus Mismatch: The vaccine may not perfectly match all circulating strains in a given season.
While not 100% effective, vaccination remains the best method to significantly reduce the risk of contracting seasonal flu, developing serious complications, and being hospitalized or dying from flu. Annual vaccination is strongly advised.
