Health Corner
Influenza Vaccination
Influenza is an infectious viral disease. It can be caused by various types of influenza viruses. In Hong Kong, the two subtypes of influenza A virus – H1N1 and H3N2, and influenza B virus, are most commonly seen. The influenza peak season in Hong Kong are normally from January to March/April, and from July to August (but is subject to the actual situation of each year). The viruses are mainly spread through droplets from the respiratory tract. It is usually self-limiting with recovery within 2 to 7 days. However, for persons with weakened immunity and if elderly get infected, more severe complications can occur, such as sinusitis, bronchitis, myocarditis, pneumonia, and at extreme situations, death. Healthy individuals can also contract with severe influenza. Getting vaccinated is one of the most effective ways to prevent influenza and its complications, as well as reduce influenza hospitalization and death.
High risk groups
- Pregnant women
- Children
- Elderly
- Chronic disease patients or patients with compromised immunity, such as chronic cardiovascular diseases, lung diseases, metabolic diseases, or renal diseases
- Healthcare workers
- Poultry workers
- Pig farmers and pig-slaughtering industry personnel
Clinical features
- Fever
- Sore throat
- Cough
- Headache
- Muscle ache
- Runny nose
- Fatigue
Vaccination
- Trivalent inactivated influenza vaccine
- Quadrivalent inactivated influenza vaccine
| Trivalent inactivated influenza vaccine | Quadrivalent inactivated influenza vaccine | |
|---|---|---|
| Preventive against | 3 types of influenza viruses | 4 types of influenza viruses (2 A viruses and 2 B virus) |
| Vaccine composition type | Inactivated vaccine | |
| Applicability | Suitable from the age of 6 months or above (Except for those with sensitive symptoms to vaccine ingredients) | |
| Method of administration | Intramuscular injection/subcutaneous injection | Intramuscular injection/subcutaneous injection |
Aged between 6 months and before 9 years: 1 to 2 dose (first-time vaccination will require 2 doses and at least 4 weeks apart) | Aged between 6 months and before 9 years: 1 to 2 dose (first-time vaccination will require 2 doses and at least 4 weeks apart) | |
| Aged 9 years or above: 1 dose | Aged 9 years or above: 1 dose | |
| Side effects | Side effects are mostly temporary and can include soreness, redness and swelling around the injection site or fever | Side effects are mostly temporary and can include soreness, redness and swelling around the injection site or fever |
Frequently Asked Questions
- Q: Will the seasonal influenza vaccine work right away?
A: No. It takes about two weeks after vaccination for antibodies to develop in the body and provide protection against influenza virus infection. For prevention against influenza, vaccinated individuals should maintain good personal and environmental hygiene practices, balanced diet, regular exercise, adequate rest and no smoking. - Q: Is it necessary to get vaccinated against seasonal influenza every year?
A: Yes. The circulating seasonal influenza strains may change from time to time. In accordance with the circulating strains, the seasonal influenza vaccine composition is updated every year to enhance protection. - Q: Do influenza vaccines in Hong Kong contain mercury or aluminum?
A: The influenza vaccine currently available in Hong Kong does not contain mercury or aluminum. - Q: Will I still be infected by influenza after vaccinating?
A: The vaccination cannot provide 100% protection, but has been shown to be effective in lowering risks of infection, complications, and death. There are several reasons why people may still get infected after vaccinating:
- It takes about 2 weeks for the body to develop antibodies to protect against the viruses, so if someone gets infected before or soon after the vaccination, the protective effect of the vaccine may have not yet been developed.
Related Information:
Influenza Vaccination Service
