As the influenza virus mutates frequently and different strains are predominant each year, it is important to get vaccinated with a new flu vaccine each year to maintain protection. Following the announcement of the World Health Organization (WHO) recommended strains for the flu season, vaccine manufactures produce the flu vaccine annually. For years, flu vaccines have been trivalent, which is designed to protect against three different flu viruses – two A viruses and one B virus.
The quadrivalent flu vaccine is designed to protect against four different flu viruses – two influenza A viruses and two influenza B viruses. Thus, quadrivalent flu vaccine may give broader protection. Quadrivalent flu vaccine has been registered in Hong Kong for people aged above 6 months.
The vaccine should be given well before the peak flu season (which is January to March & July to August in Hong Kong) to ensure its maximum effectiveness as the vaccine takes 2-3 weeks to confer protection.
Who should have higher priority for seasonal influenza vaccination?
World Health Organization (WHO) recommends the following priority groups for seasonal influenza vaccination:
- Pregnant women
- Children between the age of 6 months to 5 years
- Persons aged 65 years or above
- Health care workers
- Persons with chronic medical problems
| Virus strains in vaccine | World Health Organization (WHO) recommended that influenza vaccine for use in the 2020-2021 influenza season (northern hemisphere winter) contain the following: • A/Guangdong - Maonan/SWL 1536/2018 (H1N1)pdm09-like virus • A/Hong Kong/2671/2019 (H3N2)-like virus • B/Washington/02/2019(Victoria lineage)-like virus • B/Phuket/3073/2013(Yamagata lineage)-like virus |
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| Dosage | Children aged 6 months to aged below 9 years old | Two doses of Quadrivalent, with at least 4 weeks intervals after first dose (Only one dose is required if the children have been vaccinated in the past years) |
| People aged 9 years old or above | Only one dose of Quadrivalent | |
| Possible reaction / precautions after injection | 1) Some participants may have local reactions like soreness, redness or swelling. Low‐grade fever also may occur. 2) Drink enough water, keep warm, have sufficient rest and sleep, have a regular exercise and eat a balanced diet. |
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According to Hong Kong Department of Health Instructions:
* People with chronic medical problems mainly refer to those who have chronic cardiovascular (except hypertension without complication), lung, metabolic or kidney diseases, obesity# (BMI 30 or above), who are immunocompromised^, children and adolescents (aged 6 months to 18 years) on long-term aspirin therapy, and those with chronic neurological condition that can compromise respiratory function or the handling of respiratory secretions or that can increase the risk for aspiration or those who lack the ability to care for themselves.
# Obesity is considered as an independent risk factor for influenza complication and thus people with BMI 30 or above are included in the priority groups for seasonal influenza vaccination.
^ People who are immunocompromised refer to those with a weakened immune system due to disease (such as HIV/AIDS) or treatment (such as cancer treatment).
Members of the public can consult their family doctors to receive seasonal influenza vaccination for personal protection.
Who should NOT be vaccinated?
• People who are allergic to a previous dose of influenza vaccine or other vaccine components (e.g. neomycin or polymyxin)
• Individuals with diagnosed or suspected egg allergy
• Persons with a history of Guillain-Barré Syndrome (GBS) developed within 6 weeks after receiving influenza vaccine
• Children less than 6 months of age (influenza vaccine is not approved for this age group), andPeople who have a moderate-to-severe illness with a fever (they should wait until they recover to get vaccinated.)