2004-10-27
What is influenza?
Influenza is a viral infection characterized by the abrupt onset of fever, sore throat, cough, headache, muscle aches, runny nose, and general tiredness. The most common route of infection is through the respiratory tract. It is usually a self-limiting disease with recovery in two to seven days. However, it can be a serious illness to the weak and frail, such as elderly persons, and may be complicated by bronchitis, pneumonia, and even death in the most serious cases. Influenza can be caused by different types of viruses, and occurs most commonly around January to March and July to August in Hong Kong.
Why the influenza vaccine is important?
Influenza occurs in Hong Kong throughout the year with seasonal peaks most commonly in February and March, sometimes July and August. Influenza causes significant disease burden in some population groups where it is associated with increased risk of complications. Influenza vaccination is important because it is one of the effective means in preventing influenza and its complications. Therefore influenza vaccination to special groups is recommended by the Scientific Committee on Vaccine Preventable Diseases.
When to get vaccinated?
As the usual peak influenza season in Hong Kong is between January and March, the Scientific Committee on Vaccine Preventable Diseases recommends that the influenza vaccination to be given before the coming of next peak influenza season.
What type of influenza vaccine would be provided this year?
Influenza vaccine is prepared according to the prevalence of strains in the community each year, as recommended by the World Health Organisation. The viral-strain composition recommended for the vaccination programme in 2004/05 is as follows:
*A/New Caledonia/20/99(H1N1)-like virus
*A/Fujian/411/2002(H3N2)-like virus
*B/Shanghai/361/2002-like virus
Who should not receive flu vaccination?
Those who are allergic to eggs, neomycin or a previous dose of influenza vaccine are not suitable to have the influenza vaccination. Those with bleeding disorders or on warfarin may receive the vaccine by deep subcutaneous injection. Those who suffer from an acute febrile illness on the day of vaccination may receive the vaccine when they recover. The vaccine can be given on the same day as other types of vaccines.
Does the vaccine cause influenza?
The viruses in the vaccine are inactivated, therefore the vaccine cannot cause influenza. However, some people do develop side effects after vaccination.
What are the possible side effects of the vaccine?
Influenza vaccine is usually well tolerated apart from occasional soreness at the injection site. The recipient may experience fever, muscle and joint pains, and tiredness beginning 6 to 12 hours after vaccination and lasting up to two days. Immediate severe allergic reactions like hives, swelling of the lips or tongue, and difficulties in breathing are rare and require emergency consultation. If fever persists despite taking paracetamol, or there are other symptoms or reactions, please consult a doctor.
Does the vaccine work right away?
No. It takes about two weeks after vaccination for antibodies to develop in the body and provide protection against influenza virus infection.
How long will the protection from the vaccine last?
The vaccine currently in use helps reduce the chance of influenza and its complications, but it does not offer 100% protection. The immunity built up in the vaccinated person will decline over time and may be too low to provide protection after one year. Vaccinated persons may still develop influenza, especially when the circulating influenza viruses differ significantly from the vaccine strains. For prevention against influenza, vaccinated persons still need to maintain good personal and environmental hygiene practices, balanced diet, regular exercise, adequate rest, and avoid smoking.
Should I need to get vaccinated for influenza every year?
Yes. The fact that influenza viruses change from year to year implies:
(1) The immunity built up from having the influenza caused by one virus strain does not always provide protection when a new strain is circulating.
(2) Immunity to the disease declines over time and may be too low to provide protection after one year.