About Influenza

Influenza (flu) is an acute illness of the respiratory tract caused by influenza viruses. It is usually more common in periods from January to March and from July to August in Hong Kong. New subtype variants appear from time to time and at irregular intervals. Antigenic drifts (minor changes) of influenza viruses lead to the emergence of new viral strains every year. These minor changes cause seasonal influenza and explain why reformulation of the influenza vaccine is required every year.

Clinical Features
For healthy individuals, seasonal influenza is usually self-limiting with recovery in 2 – 7 days. Symptoms may include fever, cough, sore throat, runny nose, muscle pain, fatigue and headache; some may also have vomiting and diarrhoea.

Cough is often severe and prolonged but fever and other symptoms generally resolve in 5 – 7 days. However, influenza can be a serious illness to the weak and frail or elderly people, and may be complicated by bronchitis, chest infection or even death.

Mode of Transmission
Influenza viruses mainly spread through droplets when infected people cough, sneeze or talk. The infection may also spread by direct contact with the secretions of infected persons.


Seasonal influenza vaccination
  • The vaccine is safe and effective in preventing seasonal influenza and its complications
  • As serious influenza can occur even in healthy individuals, members of the public can consult their family doctors to receive seasonal influenza vaccination for personal protection. Usually, it is suggested that vaccination should be received in autumn every year. About 2 weeks after vaccination, the body will develop a sufficient level of antibodies to protect against influenza virus infection
  • Emergence of new strains occurs from time to time at irregular intervals, which may cause outbreaks. Therefore, WHO recommends appropriate formulation of influenza vaccine for every influenza season
Personal hygiene
  • Wash hands with liquid soap and water properly
  • When hands are not visibly soiled, clean them with 70 – 80% alcohol-based handrub
  • Cover nose and mouth when sneezing or coughing
  • Dispose of soiled tissue paper properly in a lidded rubbish bin
  • Wash hands thoroughly after sneezing or coughing
  • Put on a surgical mask when having respiratory symptoms
Environmental hygiene
  • Maintain good indoor ventilation
  • When influenza is prevalent, avoid going to crowded or poorly ventilated public places

In addition, members of the public should also maintain balanced diet, exercise regularly, take adequate rest, do not smoke and avoid overstress.

Ref : www.chp.gov.hk
last update:10 Aug 2018